To provide a spark ignition type engine preventing failure of engine starting.

In this spark ignition type engine in which fuel gas is supplied from a fuel gas supply source 1 to a fuel mixer 2, a pressure lock valve 3 is arranged between the fuel gas supply source 1 and the fuel mixer 2, the pressure lock valve 3 is communicated with the intake downstream side of the throttle valve 4 of the fuel mixer 2, and the pressure lock valve 3 shuts off fuel supply to the fuel mixer 2 on the basis of such a state that the downstream intake negative pressure of the throttle valve 4 is reduced when an engine is stalled, the choke valve 5 is arranged on the intake upstream side of the fuel mixer 2, the choke valve 5 is connected interlockingly to a valve system actuator 6, the valve system actuator 6 is linked with a control means 7, the control means 7 is linked with an engine rotational speed detecting means 8, and shutoff by the pressure lock valve 3 is canceled by narrowing the opening of the choke valve 5 according as a cranking speed is lower by the control of the control means 7 when starting the engine.