Provided is a sensorless electric motor control device capable of reducing the time from receiving a start-up signal until the rotor reaches a target rotation speed by completing a rotor phase detection before receiving the start-up signal. The control device for an electric motor (10) comprises: an inverter (11) for driving the electric motor (10) having no sensor; and a first processing unit (18) that is a phase detection unit for allowing the inverter (11) to perform a phase detection for setting a rotor magnetic pole at a predetermined position with respect to the stator of the electric motor (10) before the inverter (11) receives a start-up signal for starting up the electric motor (10).
