To provide a methane fermentation method and an apparatus which can perform methane fermentation stably for a long time by preventing an organic waste feeding line from being clogged.

Electromagnetic induction type conductance meters E1, E2 measuring the electric conductivity of the organic waste circulating in the feed lines and a cleaning means cleaning the insides of the feed lines are arranged in the feed lines L1, L6 of the organic waste. The cleaning means carries out methane fermentation by using the apparatus for methane fermentation designed to clean the feed lines when the measured values of the electric conductivity E1, E2 fall bellow the predetermined value, and the inside of the feed lines is cleaned when the measured values of the electric conductivity of the organic waste circulating in the feed lines fall below the predetermined value.