To provide a water supply device having as a motor for driving a pump a brushless motor having a permanent magnet in a rotor which can prevent pump shutoff operation while surely stopping a pump at the step out without interfering with usual operation of a pump.

The water supply device equipped with an inverter 2 for controlling rotation speed of the brushless motor while supplying driving power to a motor pump whose driving motor is the brushless motor. The water supply device is provided with a current detector 23, a frequency detector 21, a step-out detecting reference current value table 20, a step out detecting reference current value acquiring device 22 and a comparator 24. The supply device is provided with a control means for stopping the motor pump 3 when judging that the detected current value of the current detector 23 is larger than the step-out detecting reference current value acquired from the step-out detecting reference current value table 20 on the basis of the detected frequency of the frequency detector 21.