To avoid the step-out of a brushless motor when a restarting condition is satisfied during an inertia rotation after the brushless motor is directed to stop until a rotor stops rotating, in a control device of an electric water pump including the brushless motor of a sensorless type.

When the restarting condition of the brushless motor is satisfied (S5) during the inertia rotation after the brushless motor is directed to stop until the rotor of the brushless motor stops rotating, the control device prohibits the restarting until the rotor stops rotating.