PURPOSE: To prevent the wild run of a vehicle at what is equipped with a generator which is driven by a vehicle carried engine and generates alternating electric power in frequency for business, by releasing an idle up control at the time of the release of a brake and at the time of the detection of the non-neutral state of a transmission.

CONSTITUTION: An alternating current dynamo 1 driven by an engine is constituted with an armature winding consisting of low pressure windings 11a-11c and high pressure windings 12a-12c, a three phase all wave rectifier 13, an auxiliary rectifier 15 and a voltage regulator 16. And at the idling operation state of the engine, a throttle valve 105 is opened by controlling an actuator 103 by means of a controller 102, and a predetermined alternating current output from the dynamo 1 is generated by raising the revolution number of idling. In this instance, control is arranged so as to release an idling up control when a brake is released due to a side brake switch 8 being 'OFF', or when a transmission is not in a neutral position due to a neutral switch 9 being 'OFF'.