To validly treat sludge and woody biomass by methane fermentation treatment.

A methane fermentation treatment method for organic waste for carrying out wet type methane fermentation to sludge and woody biomass includes: a pre-treatment process of mixing woody biomass under pressurization for crushing and swelling; a tempering process of mixing the woody biomass after the pre-treatment process with at least a portion of the sludge such that the moisture content of the woody biomass is equal to or more than 90 mass% and equal to or less than 98 mass%; a methane fermentation process of adjusting the mixture of the sludge and the woody biomass after the tempering process such that the content of the woody biomass is equal to or more than 0.1 mass% and equal to or less than 3 mass% of the whole amount of mixture in a methane fermentation tank, and then carrying out methane fermentation, and collecting methane gas; and a solid disposal process of disposing a solid by dehydrating the fermentation residue after methane fermentation.