To stably perform combustion of in a main combustion chamber irrespective of an operation state and variations among cylinders to secure engine performance and reduce operation costs with reduced use amount of combustion gas, by controlling an opening time of a solenoid valve for each cylinder on the basis of temperature data in a sub-chamber so that an air-fuel ratio in the sub-chamber becomes a target air-fuel ratio for obtaining stable combustion in the sub-chamber by a spark plug.

In this sub-chamber gas supply control device 5 for a sub-chamber type gas engine 50 individually introducing fuel gas into sub-chambers 1 of a multi-cylinder gas engine by a sub-chamber gas supply solenoid valve 52 and igniting it by a spark plug 9, the sub-chamber gas supply control device includes: a sub-chamber internal temperature detection means 60 for detecting a temperature in the sub-chamber 1 or in the vicinity of the sub-chamber 1; and a sub-chamber gas supply control means 66 for controlling an opening time of the sub-chamber gas supply solenoid valve 52 so that the temperature in the sub-chamber 1 is maintained within a predetermined range and an air excess ratio inside the sub-chamber becomes a predetermined value.