To provide a technique for efficiently and conveniently treating solid organic matter that is requested to be effectively utilized and converting it to energy.

The solid organic matter is subjected to a dispersion process including a pulverizing step where the solid organic matter is mixed with methane fermentation sludge and the obtained mixture is crushed and pulverized by a cutter pump 20 and then is subjected to a methane fermentation process for carrying out methane fermentation of dispersed treated matter.