PURPOSE: To prevent any drop in the engine speed in time of a variation in load, by installing a device capable of controlling the operation of a generator according to the engine speed and a throttle valve controlling device, altering the setting speed according to a state of driving, both in a cylinder-number control engine carrying the generator.

CONSTITUTION: A control device, which controls both a throttle valve 2 in a multicylinder engine and a regulator for an engine driven generator, compares the desired engine speed set at a desired value setting circuit 31 on the basis of signals out of an air conditioner switch CS and an off-cylinder discrimination circuit 32 with a signal out of an engine speed sensor D, then alters a duty ratio for a pulse signal out of a comparator 25 according to the engine speed, and controls the duration of power generation in the generator via a transistor 27. In addition, the device 18 opens or shuts the throttle valve 2 via an opener 8 by means of deflection between the second desired engine speed being set according to a state of driving and the actual engine speed, and when electric load increases, the device 18 regulates the engine speed to a final desired value by the throttle valve after regulating the engine speed in a way of generated energy control.