TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Conditions: Two or more types of fluids are used, with at least one fluid containing titanium compound(s). A dispersing agent is included in the fluid(s). At least one type of fluid is a reverse micellar solution obtained by adding a dispersing agent and water to an organic solvent. At least one type of fluid is either among the fluids of that except the above among the non-aqueous solution containing a titanium compound, an aqueous solution containing a titanium compound, and a reverse micellar solution containing a titanium compound. The titanium compound is hydrolyzed in the thin film fluid, to obtain titanium-dioxide ultrafine particles. A metallic compound containing an element formed into solid solution in titanium dioxide, apart from the titanium compound, is included in the fluid. A supply-flow channel independent of the flow path where to-be-processed fluid of specified pressure is poured, is provided. The processing surface(s) is equipped with an opening portion which leads to the supply-flow channel. A thin film fluid is formed by introducing to-be-processed fluid(s) from the supply-flow channel between the processing surfaces. The reaction material contained in each to-be-processed fluid, and a different to-be-processed fluid are reacted by uniformly mixing within the liquid film. Heating is carried out between the processing surfaces, or UV ray is irradiated between the surfaces, or ultrasonic energy is provided between the surfaces.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Compounds: The metallic compound is metal alkoxide or metal salt of aluminum, barium, magnesium, calcium, lanthanum, iron, silicon, zirconium, lead, tin, zinc, cadmium, arsenic, gallium, strontium, bismuth, tantalum, selenium, tellurium, hafnium, magnesium, nickel, manganese, cobalt, sulfur, chromium, vanadium, germanium, lithium and/or boron. Glass containing silicon oxide and/or silicon, a substance containing complex oxide of silicon, and/or dissolution of the above mixtures and/or solid solution in hydrochloric acid, sulfuric acid, and/or nitric acid are added to the fluid. A pH adjuster and hydrogen peroxide are added to the fluid(s). After adding acid containing chloride, such as hydrochloric acid, to the fluid(s), Broensted base, such as nitrate ion and phosphate ion, are added to the fluid to which acid is added, or to a different fluid. Aluminum oxide, zirconium oxide, silicon oxide, antimony oxide, tin oxide, and/or zinc oxide are added to the fluid(s). Apart from titanium compound, calcium carbonate and phosphoric acid, or hydroxyapatite, are added to the fluid(s). Preferred Property: The obtained titanium-dioxide ultrafine particles have a volume average particle diameter of 0.5-1000 nm.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Compounds: The titanium compound is tetraalkoxytitanium or its derivative(s), such as tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium, tetra-n-butoxytitanium, tetra-isobutoxytitanium, tetra-t-butoxytitanium, titanium tetrachloride, titanyl sulfate, titanium citrate, and/or titanium tetranitrate. Ethyleneglycol, propyleneglycol, trimethyleneglycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-butene-1,4-diol, hexyleneglycol, octyleneglycol, glycerin, hexaglycerol, and/or 1,2,6-hexanetriol are added to the fluid. An organometallic compound, such as metal chelate compound, cyclic metal oligomer, or metal alkoxide containing aluminum, zirconium, antimony, tin, zinc and/or titanium is added to the fluid(s). Polymerizable monomers chosen from derivative of styrene, chlorostyrene, and styrene, such as methylstyrene, acrylic acid and derivative of acrylic acid, such as methylacrylate, and methacrylic acid and derivative of methacrylic acid, such as methylmethacrylate, are added to the fluid(s). Electrical charge controlling agents which are not resins, such as metal complex of organic compound having a carboxyl group or a nitrogen-containing group, a calixarene compound, a metal-containing dye, and nigrosine, are added.    TECHNOLOGY FOCUS - POLYMERS - Preferred Compounds: The dispersing agent is cellulose, such as starch, methylcellulose and ethylcellulose, polymer dispersion stabilizer, such as polyacrylimide, polyethyleneoxide, and poly(hydroxystearic acid-g-methylmethacrylate co-methacrylic acid) copolymer, nonionic surfactant, anionic surfactant, amphiphilic surfactant, or polyphosphoric acid, such as hexaphosphoric acid, octaphosphoric acid, tetraphosphoric acid, and triphosphoric acid, polymeric organic acid, such as acetic acid, acrylic acid, and methacrylic acid, polymeric organic matter, such as polyvinylpyrrolidone, polyvinyl alcohol, and sodium hexametaphosphate, and/or diisooctylsodium sulfosuccinate. Electrical charge controlling agents, such as quaternary ammonium group- or quaternary ammonium salt group-containing copolymer, sulfonic acid group- or sulfonate group-containing copolymer, and carboxylic acid group- or carboxylate salt group-containing copolymer, are added.