To provide a control method for an auxiliary chamber type gas engine for preventing increase of operation pressure of a check valve to prevent improper operation of the check valve in a combustion auxiliary chamber.

In this auxiliary chamber type gas engine, each fuel gas supply pressure to a fuel gas injection device I1 for a main chamber and a fuel gas injection device I2 for the auxiliary chamber is controlled based on extraction of lean mixture pressure from an air supply pressure sensor S3 in an air supply passage 3 on the downstream side of a throttle 5.