A power supply device, comprising: an electronic switch (T1) provided on a wiring which connects a DC power supply (VB) to a motor load (M1); a driving portion that controls the electronic switch (T1) with PWM to drive the motor load (M1); a semiconductor element (T2) that has a parasitic diode (Dp) and is disposed in parallel to the motor load (M1) so that a forward direction of the parasitic diode (Dp) is in opposite to a flowing direction of a current (IM) flowing through the motor load (M1); and a control portion that controls the semiconductor element (T2) so as to be turned on during a part of a period during which the electronic switch (T1) is placed in an off state under a control with the PWM, wherein the semiconductor element (T2) is an N-type field effect transistor which includes a drain, a source, and a gate; characterized in that the control portion includes a serial connection circuit which is formed by a first resistor (R2) and a transistor (T3); the serial connection circuit is disposed between the DC power supply (VB) and the ground; and a control input terminal of the transistor (T3) is connected to a first connection point (a) for connecting between the electronic switch (T1) and the motor load (M1), a second connection point (b) for connecting between the first resistor (R2) and the transistor (T3) is connected to the ground via a serial connection circuit formed by a capacitor (C1) and a second resistor (R3), and a third connection point (c) for connecting between the capacitor (C1) and the second resistor (R3) is connected to the gate of the semiconductor element (T2). an electronic switch (T1) provided on a wiring which connects a DC power supply (VB) to a motor load (M1); a driving portion that controls the electronic switch (T1) with PWM to drive the motor load (M1); a semiconductor element (T2) that has a parasitic diode (Dp) and is disposed in parallel to the motor load (M1) so that a forward direction of the parasitic diode (Dp) is in opposite to a flowing direction of a current (IM) flowing through the motor load (M1); and a control portion that controls the semiconductor element (T2) so as to be turned on during a part of a period during which the electronic switch (T1) is placed in an off state under a control with the PWM, wherein the semiconductor element (T2) is an N-type field effect transistor which includes a drain, a source, and a gate; characterized in that the control portion includes a serial connection circuit which is formed by a first resistor (R2) and a transistor (T3); the serial connection circuit is disposed between the DC power supply (VB) and the ground; and a control input terminal of the transistor (T3) is connected to a first connection point (a) for connecting between the electronic switch (T1) and the motor load (M1), a second connection point (b) for connecting between the first resistor (R2) and the transistor (T3) is connected to the ground via a serial connection circuit formed by a capacitor (C1) and a second resistor (R3), and a third connection point (c) for connecting between the capacitor (C1) and the second resistor (R3) is connected to the gate of the semiconductor element (T2). <EOS>