An IIS system that performs control related to intermittent stopping of engine operation by idling stop control is applied to an internal combustion engine including a VVT mechanism that makes the valve timing of an engine valve variable and has an intermediate lock mechanism that mechanically locks the valve timing at an intermediate lock position between a most retarded position and a most advanced position. The IIS system is configured to inhibit the engine operation from being intermittently stopped at the occurrence of a failure of the VVT mechanism to avoid the internal combustion engine from being prevented from being restarted after the intermittent stop depending on the occurrence of the failure of the VVT mechanism.