In an electric water pump for circulating cooling water of an engine mounted on a vehicle or similar, a time interval to switch energized phase of a pump motor is set to longer than a time interval during a normal flow rate control (during a flow rate control at a flow rate equal to or more than a flow rate where an electromotive force generated at a non-energized phase is detectable). In the case where a pump discharge pressure (or a water temperature of the cooling water) repeatedly increases and decreases in this extremely low flow rate state, it is determined that the electric water pump normally rotates as required. This allows providing the extremely low flow rate state between a water stop state and a water circulation state in a control for stop of water in an engine cooling system.