There is provided an apparatus for controlling an electric compressor, which can actuate the electric compressor rapidly through a simpler and lower-cost configuration while achieving reduction in weight, cost, and assembling time of the electric compressor. In the case where a pressure difference between the inlet side and the outlet side of the compressor body is present when a motor of the electric compressor is actuated, the motor is actuated at a number of revolutions lower than that in the normal mode. Thereby, even if a refrigerant has been liquefied on the outlet side of the compressor body, for example, the motor can be actuated by performing such action as to push out the liquefied refrigerant. In this case, the number of revolutions of the motor is increased by being changed stepwise or linearly, by which the number of revolutions of the motor is caused to reach a required number of revolutions as early as possible while surely performing the actuation.