Engine rotational speed control apparatus

A rotational speed control apparatus for an engine, the engine configured to drive a compressor that compresses a cooling medium for air conditioning, and the engine includes an ignition plug, the rotational speed control apparatus comprising:

• an electronic control unit configured to:
• (a) correct a torque of the engine, by adjusting an ignition timing of the ignition plug of the engine, through feedback such that a rotational speed of the engine during idle operation becomes close to a target rotational speed;
• and
• (b) adjust the ignition timing such that a reserve torque that is ensured is larger when a first changeover is started than when a second changeover is started, the first changeover being a changeover from a stopped state of the compressor to a driven state of the compressor, the second changeover being a changeover from the driven state of the compressor to the stopped state of the compressor, the reserve torque being a reserve of increase in the torque of the engine resulting from advancement of the ignition timing.