Abstract: To make organic fertilizer by performing fermentation treatment of organic waste containing a large quantity of water content such as garbage, while maintaining conditions of treatment suitable for fermentation. A fermentation treatment apparatus of organic waste according to the present invention is constituted in such a way that a steam supply pipe 3 is connected to a jacket part 2 of a fermentation tank 1 by way of reducing valves 17 and 18, and a vacuum pump 4 is connected below the jacket part 2 by way of a communicating line 27. When steam reduced in pressure lower than 100° C. is supplied into the jacket part 2, the waste housed within the fermentation tank 1 can be promptly treated with fermentation by utilizing condensation heat of steam. Furthermore, the air at a predetermined humidity is supplied into the fermentation tank 1 from the air supply part 36, so that fermentation treatment due to aerobic bacteria can be performed in a short time and efficiently.