To provide a technology for realizing operation in a wide rotation area, and to particularly provide a technology for performing speed governing control for realizing stable operation in a high load area of a low speed rotation area in the speed governing control of a gas engine.

This control device of the gas engine has a means for detecting a motive power load, a means for detecting an engine speed, a means for detecting the air-fuel ratio, and a controller, and determines control gain Kp4 corresponding to the motive power load D, the engine speed N and the air-fuel ratio G on the basis of a prestored control map 34 when performing the speed governing control of the engine speed, and performs the speed governing control of the gas engine by changing the control gain Kp4 according to the motive power load, the engine speed and the air-fuel ratio.