A methane generation system that generates methane from a first gas containing methane and carbon dioxide generated by treatment of wastewater in a wastewater treatment facility, the methane generation system includes: a controller including a processor and a memory storing a computer-executable instruction. The processor is configured to execute, an operation of calculating a reference supply amount of a third gas to be supplied to a methane generation reactor based on an amount of carbon dioxide in a first gas measured by an inlet sensor assembly, and an operation of regulating at least one of a supply amount of the first gas by a first flow rate regulator and a supply amount of the third gas by a second flow rate regulator in real time based on a concentration of at least one of carbon dioxide and hydrogen in a second gas measured by an outlet sensor assembly.