The utility model relates to a methane generating device which is characterized in that a methane generating pot is included, an output pipe of methane and a feed pipe whose top end has a pressure relief hatch are connected with the top of the methane generating pot, the upside of the feed pipe is communicated with a delivery channel which is connected with the side of the feed pipe, the bottom of the feed pipe extends down to the fluid level of materiel of the methane generating pot, a hatch on the lower end of the output pipe of methane is close to the top of the methane generating pot, an opening on the lower side of the methane generating pot is connected with a sullage pipe turning upwards. The device can continuously and automatically run off the slag, thus avoiding the manual dejecta taking. The device has the advantages of simple structure, low cost and safe and convenient use.