The content of methane gas (CH4) in biogas varies depending on livestock feed and the weather around the bioreactor, so that it will have an impact on the heat generated in the combustion chamber of the electric generator. For this reason, it is necessary to measure the content of methane gas in biogas. The information on the content of methane gas in biogas is very useful for regulating the ratio of air supply and biogas supply in maintaining the quality of the heat produced in the combustion chamber. So that the operation of the electric generator can be maintained. The methane gas content device consists of a methane gas sensor, a data processing circuit and a personal computer equipped with a GUI (Graphical User Interface), the measurement data can be integrated with the ratio control program on a PC which also functions as a controller. So that the PC can generate a control signal to adjust the ratio of air supply and biogas supply to the biogas as a power electric generator.