BIOGAS-FIRED ENGINE

[Object] is to provide a biogas-fired engine capable of sucking a biogas at a flow rate necessary for stoichiometric combustion by raising a negative suction pressure of a venturi mixer. [Solution] is a biogas-fired engine 1 fueled solely by a biogas G1 to G2 derived from organic waste, the biogas-fired engine 1 comprising: a pressure equalizing valve 30 arranged in a gas supply path 31; an A/F valve 41 arranged in the gas supply path 31 at a location downstream of the pressure equalizing valve 30; and a venturi mixer 40 arranged at a location where the gas supply path 31 joins an intake path 43, wherein the pressure equalizing valve 30 adjusts a pressure to approximately atmospheric pressure, and an area of the venturi mixer 40 is adjusted so as to provide a target air flow velocity Tas that allows the biogas G1 to G2 to be sucked at a flow rate necessary for causing predetermined combustion with a predetermined engine output P by a differential pressure between a pressure of the venturi mixer 40 and a pressure adjusted by the pressure equalizing valve 30.