To provide a sludge treatment apparatus capable of easily separating a solid component from sludge in a short time, and a sludge treatment method using it.

The sludge on the bottom or the like of a lake is dredged by a dredging ship 11 and polluted water containing this sludge is allowed to flow in a mixing tank 1 from a sludge supply port 1a through a sludge feed pipe 12. Further, the opening degree of an adjusting valve 5 is adjusted to set the stagnation time of the polluted water in the mixing tank 1 to about 30-60 sec. Then, a predetermined flocculant is supplied to the polluted water in the mixing tank 1 from a flocculant supply device 2. At this time, the diffusion spraying of the flocculant is performed using air so as to efficiently mix the polluted water with the flocculant. As the flocculant, a composition prepared by uniformly compounding 5-20 pts.wt. of a zeolite particulate material and/or 1-30 pts.wt. of a cationic flocculant with a predetermined main flocculant is used.