To provide a fuel gas metering device for a gas engine which can easily and surely perform starting of the engine.

A pressure governor 14 having a negative pressure lock mechanism 23 and a centrifugal governor 17 are provided, the negative pressure lock mechanism 23 is operated by an intake negative pressure of an engine, fuel gas is supplied to a mixer 3, also, in the case of the intake negative pressure smaller than a prescribed value, supply of fuel gas is interrupted. An electric unlock means 60 is additionally provided in the pressure governor 14, this electric unlock means 60 is associated with switching to a start position 68 of a start switch 67 of the engine, interruption of fuel gas by the negative pressure lock mechanism 23 is released.