In the embodiment, as shown in FIG. 3, when the motor 41 is activated (point in time t1), the value of the consumption current Id of the motor 41 increases rapidly right after the activation. In FIG. 3, the value of the consumption current Id increases to reach an overloaded current value Id1, which is larger than the maximum output current value Im, and the second constant voltage circuit 12 comes into the overloaded state. During an overloaded period W1 which is defined as a period in which the second constant voltage circuit 12 is in the overloaded state, the value of the second voltage V2 decreases from the steady voltage value V21 to fall below the value of the first voltage V1. As a result, part of the first current I1 of the first constant voltage circuit 11 is supplied to the motor 41 as the differential current Is. In short, in the overloaded period W1, a part, corresponding to the maximum output current value Im, of the consumption current Id is covered by the second current I2. Moreover, the differential current Is (difference obtained by subtracting the maximum output current value Im from the overloaded current value Id1) is covered by part of the first current I1.