To cleanly remove foreign matter adhering on the surface of a porous cylinder or the inner surface of a drainage reservoir tank with a simple mechanism.

This garbage disposer is equipped with a crusher 1 and a water separator 2 which separates the garbage crushed by the crusher 1 from water. The water separator 2 is equipped with the porous cylinder 4 made by forming a porous plate into a cylindrical shape, the drainage reservoir tank 10 in which the water up to a prescribed level is stored and the lower part of the porous cylinder 4 is arranged under water, air nozzles 20 for injecting the bottom of the drainage reservoir tank 10 with the air, a lifting screw 5 disposed inside the porous cylinder 4, and a motor 6 for driving the lifting screw 5. The water separator 2 lifts a mixture of garbage and water supplied to the supply port 4A of the porous cylinder 4 with the lifting screw 5 and the mixture is drained before being discharged from a discharge port 4B. The air nozzles 20 inject numberless air bubbles below the surface of the water in the drainage reservoir tank 10, and the foreign matter adhering on the porous cylinder 4 or the drainage reservoir tank 10 is removed by letting the air bubbles lift from the bottom of the drainage reservoir tank 10 upward to the outside of the porous cylinder 4.