TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Materials: The inorganic substance is silica gel, zeolite or magnesium oxide. The signal generator comprises a compound capable of discoloring upon water absorption, preferably cobalt chloride; a compound capable of releasing ion(s) upon water absorption, preferably weakly alkaline crystal each having a pH upon electrolytic dissociation of 7-12, and a pH-indicator; a compound capable of color-developing upon dissolution as a result of water absorption, preferably a dried substance containing sodium nitrite and sulfanilic acid.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The water-absorber comprises a water-absorptive component (2)capable of fixing absorbed water. The water-absorptive component comprises organic substance(s) and an inorganic substance. The water-absorber comprises a signal generator configured to generate a signal indicating water absorption. The signal is discoloration, deformation, pH change, temperature change, pressure change, magnetic change, voltage change, or material absorption-desorption. The signal is capable of being visually detected. The signal generator is so configured to control signal generation in accordance with the quantity of absorbed water. The ratio of the volume of the water-absorber after water absorption to the volume of the water-absorber before water absorption (Y/X) is greater than or equal to1.0. The water-absorber is a molded article of the water-absorptive component, or a structure comprising a substrate and the water-absorptive component. It may be a sheet-like structure. The water-absorber is arranged detachably. One sheet face of the sheet-like water-absorber is detachably stuck to at least part of the outer surface of the fuel cell cartridge. The fuel cell cartridge has a columnar shape. The water-absorber is arranged on a peripheral side face of the columnar fuel cell cartridge. The water formed in the fuel cell power generation part comprises water formed as a result of a fuel cell reaction. The fuel cell cartridge is recyclable. It comprises greater than or equal to2 water-absorbers. It further comprises a body configured to supply a fuel reserved in the fuel reservoir to the fuel cell power generation part. The body is a funnel component (4). The fuel cell power generation part, the body and the fuel cell cartridge are vertically arranged in this order from above. The fuel electrode, the solid electrolyte and the air electrode of the fuel-cell power generation part are laminated so that their lamination planes are substantially in parallel with a vertical direction.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Materials: The pH indicator is phenolphthalein or thymol blue. The compound capable of color-developing upon dissolution as a result of water absorption may be a dried substance containing N-l-naphthylethylenediamine and tartaric acid.    TECHNOLOGY FOCUS - POLYMERS - Preferred Polymers: The organic substance is a naturally-occurring polymer or a synthetic polymer. The naturally-occurring polymer is cellulose polymers, alginic acid polymers, mannan polymers, pullulan polymers or chitin-chitosan polymers. The synthetic polymer is acrylic polymers, acrylamide polymers, poly(ethylene oxide) polymers or polyester polymers.