Water contained in raw garbage introduced through a throw port is drained off by a filter member and a water-draining gate, and is drained into a drainpipe, the water having good quality. The raw garbage from which water is drained off to a sufficient degree is dry-pulverized by a pulverizer unit and is smoothly blown into the microorganism decomposition chamber through a carrier duct having a flared end, utilizing the impact force of the impeller revolving in the pulverizer unit. The dry-pulverized raw garbage that is thus conveyed is decomposed by a microorganism carrier in the microorganism decomposition chamber.