To effectively decompose garbage, and to treat it in a relatively short time.

A garbage charging port 3 is formed on a peripheral wall of a rotary drum 1, garbage is thrown into the rotary drum 1 from the charging port 3, and the charging port 3 is closed with a cover 5. Subsequently, the rotary drum 1 is driven and rotated by a rotationally driving mechanism 15 to stir chips and the garbage. The air in an air introduction pipe is introduced to the rotary drum 1, and the air in the rotary drum 1 is discharged through an air discharge pipe. The garbage is decomposed and treated by soil bacteria on the chips.