To provide a method for efficiently producing methane from a treated product obtained by blasting treatment of biomass.

The method for producing a methane gas, employed for producing the methane gas 3b from a woody biomass a such as waste broad-leafed trees, comprises following process: a solid-liquid separation of the resultant blast product is conducted after conducting the step of blasting biomass; and the resulting liquid phase is subjected to UASB (upflow anaerobic sludge blanket-type high-speed methane fermentation) treatment. The blasting treatment is conducted at higher than 210°C but not higher than 225°C.