In starting of an internal combustion engine, among a plurality of combustions of the internal combustion engine when it is assumed that an ignition timing is set to a predetermined reference ignition timing, a preceding ignition timing, which is the ignition timing for a preceding combustion through which a peak of a rotation speed of the internal combustion engine is likely to enter a predetermined resonance rotation speed range where resonance of the conveyance dependent on vibration of the internal combustion engine is induced, is set further on a delay angle side than the reference ignition timing, and a later ignition timing, which is the ignition timing for a later combustion after the preceding combustion, is set further on an advance angle side than the set preceding ignition timing so that the peak of the rotation speed of the internal combustion engine exceeds the resonance rotation speed range.