PURPOSE: To improve the restarting performance by installing a solenoid valve for opening/closing-controlling the opening of an air introducing pipe whose one edge is connected to an engine to the atmosphere and opening the solenoid valve when the engine starting operation state is in a prescribed state on restart.

CONSTITUTION: An air introducing passage 72 whose upstream side is opened into the atmosphere, making a detour around a throttle valve 22 installed in the intake passage 29 of an internal combustion engine 2, and whose downstream side communicates to the intake passage 20 on the upstream side of a flange, on the downstream side of the throttle valve 22, is installed. Further, a solenoid valve 74 for controlling the air feed quantity in the air introducing passage 72 is installed. Further, a control part 44 which performs control so that restart is enabled by introducing air into the internal combustion engine 2 by opening the solenoid valve 74 when the engine starting operation state detecting signal supplied from a starter relay 60 and a starter switch 62 on the restart of the internal combustion engine 2 is in a prescribed state, is installed. Accordingly, the restart performance is improved, and the using performance is improved.