To provide in-vehicle compression equipment capable of making compatible both the highly efficient operation of a compressor and comfortability in a cabin, and a method for controlling the on-vehicle compression equipment.

When engine speed is low, a motor (prime mover) is stopped or rotated at a low rotational frequency and a scroll compressor (the compressor) is stopped or operated at a low rotational frequency. When the engine speed is increased and reaches a high speed region, the motor is rotated at a high rotational frequency and the scroll compressor is operated at a high rotational frequency. Therefore, since the motor is rotated at the high rotational frequency and the scroll compressor is operated at the high rotational frequency only when engine noise is large, the noise of the scroll compressor is not noticeable. As a result, both the efficiency of the scroll compressor and quietness in the cabin can be secured.