Stop control system for internal combustion engine

A stop control system for an internal combustion engine, which is capable of ensuring the comfort of vehicle occupants in a vehicle compartment and improving the fuel economy of the engine along with automatic stoppage of the engine during both a cooling operation and a heating operation of an air conditioner. When the engine is automatically stopped, the stop control system sets a target blowout temperature which is a target value of the temperature of air blown out from the air conditioner into a vehicle compartment, and acquires a fan voltage indicative of the air volume blown by a fan of the air conditioner. Further, the stop control system calculates stop allowable time based on the target blowout temperature and the fan voltage, and restarts the engine when engine stoppage time period (stoppage time period-counting timer value) has reached the stop allowable time.