An object of the present invention is to provide a starting device for a gas internal combustion engine whereby non-combusted gas accumulating in the gas internal combustion engine and an exhaust channel is discharged during ignition startup of the gas engine and abnormal combustion is prevented so as to improve safety, breakage prevention, durability and reliability. An exhaust purge device for a gas internal combustion engine 1 which operates using flammable gas as fuel includes an exhaust channel 16 forming an exhaust channel of the gas internal combustion engine 1, a blast pipe 71 connected to an upstream portion of the exhaust pipe at one end, an exhaust purge fan 7 connected to another end of the blast pipe 71 and configured to send ambient air to the exhaust channel 16, and a control device 2 for performing a control to drive the exhaust purge fan 7. The control device 2 includes: a purge-fan operation determination part 24 configured to determine whether the exhaust purge fan 7 has been operated; and a purge-fan operation command part 28 configured to operate the exhaust purge fan for a set time if it is determined that the exhaust purge fan has not been operated.