The present invention comprises a seat belt fastening detector (12) that detects a fastening state or a non-fastening state of a driver's seat belt, a door open/close detector (13) that detects an open state and a closed state of a vehicle door, and control means (11) that restarts, in a stopped state of the engine (2) caused by an idling stop control, the engine when a predetermined restart condition is satisfied. In cases where the vehicle door is in the open state with the driver's seat belt being in the fastening state or the vehicle door is in the closed state with the driver's seat belt being in the non-fastening state, the engine is allowed to be restarted when the restart condition is satisfied. In a case where the vehicle door is in the open state and the driver's seat belt is in the non-fastening state, the engine will be prohibited from being restarted even if the predetermined restart condition is satisfied.