In a compressor control system for a vehicle air conditioner, a hybrid ECU of the vehicle controls a rotation speed of a compressor electric motor. In this case, an output circuit, which outputs a driving signal for driving the compressor electric motor, only needs to be newly provided in the hybrid ECU when a hybrid vehicle or an electric vehicle is manufactured based on an engine vehicle. Therefore, a high cost is not caused even when the output circuit is provided in the hybrid ECU which should be newly designed and manufactured. In addition, because the output circuit does not need to be provided in an air-conditioning ECU which is an existing component of the engine vehicle, the air-conditioning ECU in the engine vehicle can be directly applied to that in the hybrid vehicle without a substantial hardware change. Therefore, design cost can be reduced.