To appropriately control the engine idle speed at the time of starting a compressor or during the operation thereof, and to securely prevent unexpected lowering and increase of rotation.

An engine idle speed control device to be loaded on a vehicle provided with an air conditioning cycle 10, which includes a compressor 11 to be driven by an engine, and for controlling the engine idle speed with a revolution control means 41 in response to operation/stop of the compressor 11 is provided with detecting means 2, 3 for detecting the physical quantity corresponding to the torque of the compressor 11, a computing means 31 for obtaining the control value for controlling the revolution control means 41 on the basis of the output from the detecting means 2, 3, and a control means for controlling the revolution control means 41 on the basis of the control value, which is obtained by the computing means 31, at the time of starting and/or operating the compressor 11.