Abstract: To treat organic sludge while keeping facility costs, cement production efficiency, and a reduction in clinker production amount to a minimum. An organic sludge treatment device includes: a fractionation device 7 that fractionates a preheated raw material R2 from a preheater cyclone 4C excluding a bottommost cyclone of a cement burning device 1; a mixing device 8 that mixes an organic sludge S with the fractionated preheated raw material, and that dries the organic sludge using sensible heat of the preheated raw material; and a supply device (mixture chute 12, double-flap damper 13, shut damper 14) that supplies a mixture M from the mixing device to a calciner furnace 5 of the cement burning device or to a duct disposed between a kiln inlet portion of a cement kiln 2 and the calciner furnace.