NOVELTY - A biomass is suspended in high-temperature high-pressure water maintained at a pressure, which is more than vapor pressure of water, at 100-250degreesC to obtain low concentrated slurry. Biomass is further added to the low concentrated slurry, to obtain highly concentrated biomass slurry.    USE - For manufacturing highly concentrated biomass slurry used for manufacturing fuel gas and solid fuel (both claimed) for thermal power station and electric power generation, and as coal-substitute material for blast furnace.    ADVANTAGE - The highly concentrated slurry having large amount of biomass is obtained, and a fuel is efficiently and economically recovered from processed biomass.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) highly concentrated biomass slurry manufactured by the above method and having biomass concentration of 10 mass% or more;    (2) manufacture of fuel gas. The highly concentrated biomass slurry used as raw material is heated at 150-350degreesC. The biomass in the slurry is modified at a pressure, which is more than the vapor pressure of water. An aqueous solution is recovered from the highly concentrated slurry, which is passed through the modification process. The recovered aqueous solution is gasified to obtain fuel gas;    (3) manufacture of solid fuel, which involves recovering a water-insoluble component from the highly concentrated biomass slurry, which is passed through the modification process, and dehydrating the recovered water-insoluble component; and    (4) manufacturing apparatus (11) of highly concentrated biomass slurry, which has a grinder (2) for pulverizing the biomass, a supply unit (3) for supplying the ground material to slurry manufacturing container, a water supply unit (4) for supplying water to the container, a mixing unit (5) for mix-suspending of the ground material with high-temperature high-pressure water, and a heating unit (6) for heating the water and/or the slurry in the container.    DESCRIPTION OF DRAWING(S) - The figure shows an explanatory drawing of highly concentrated biomass slurry manufacturing apparatus. (Drawing includes non-English language text).    slurry manufacturing container (1)    grinder (2)    biomass supply unit (3)    water supply unit (4)    stirring unit (5)    heating unit (6)    slurry manufacturing apparatus (11)