A power supply device configured to be connected to a battery and to a load to which power is supplied from the battery, the power supply device comprising: a capacitor; a first switch configured to switch a connection state between the battery and the capacitor; a second switch configured to switch a connection state between the capacitor and the load; and a control unit configured to detect abnormality of the battery; characterized in that the first switch includes: a second semiconductor switch and a third semiconductor switch connected in series between the battery and the capacitor; a series circuit of a first semiconductor switch and a resistor, wherein the series circuit is connected in parallel with the second semiconductor switch; wherein in the first semiconductor switch and the second semiconductor switch, an anode of a parasitic diode is disposed on a side of the battery, and in the third semiconductor switch, the anode of the parasitic diode is arranged on a side of the capacitor; and the control unit is further configured to detect a state of charge of the capacitor, wherein when not detecting abnormality of the battery, the control unit is configured to turn on the first switch and to turn off the second switch when the capacitor is not fully charged, wherein the first semiconductor switch and the third semiconductor switch are turned on while the second semiconductor switch is turned on after lapse of a predetermined time since the first semiconductor switch and the third semiconductor switch are turned on, and to maintain the first switch on after the capacitor is fully charged, and wherein when detecting the abnormality of the battery, the control unit is configured to turn off the first switch, wherein the first, second and third semiconductor switches (SW1, SW2, SW3) are turned off, and to turn on the second switch. a capacitor; a first switch configured to switch a connection state between the battery and the capacitor; a second switch configured to switch a connection state between the capacitor and the load; and a control unit configured to detect abnormality of the battery; characterized in that the first switch includes: a second semiconductor switch and a third semiconductor switch connected in series between the battery and the capacitor; a series circuit of a first semiconductor switch and a resistor, wherein the series circuit is connected in parallel with the second semiconductor switch; wherein in the first semiconductor switch and the second semiconductor switch, an anode of a parasitic diode is disposed on a side of the battery, and in the third semiconductor switch, the anode of the parasitic diode is arranged on a side of the capacitor; and the control unit is further configured to detect a state of charge of the capacitor, wherein when not detecting abnormality of the battery, the control unit is configured to turn on the first switch and to turn off the second switch when the capacitor is not fully charged, wherein the first semiconductor switch and the third semiconductor switch are turned on while the second semiconductor switch is turned on after lapse of a predetermined time since the first semiconductor switch and the third semiconductor switch are turned on, and to maintain the first switch on after the capacitor is fully charged, and wherein when detecting the abnormality of the battery, the control unit is configured to turn off the first switch, wherein the first, second and third semiconductor switches (SW1, SW2, SW3) are turned off, and to turn on the second switch. a second semiconductor switch and a third semiconductor switch connected in series between the battery and the capacitor; a series circuit of a first semiconductor switch and a resistor, wherein the series circuit is connected in parallel with the second semiconductor switch; wherein in the first semiconductor switch and the second semiconductor switch, an anode of a parasitic diode is disposed on a side of the battery, and in the third semiconductor switch, the anode of the parasitic diode is arranged on a side of the capacitor; and the control unit is further configured to detect a state of charge of the capacitor, wherein when not detecting abnormality of the battery, the control unit is configured to turn on the first switch and to turn off the second switch when the capacitor is not fully charged, wherein the first semiconductor switch and the third semiconductor switch are turned on while the second semiconductor switch is turned on after lapse of a predetermined time since the first semiconductor switch and the third semiconductor switch are turned on, and to maintain the first switch on after the capacitor is fully charged, and wherein when detecting the abnormality of the battery, the control unit is configured to turn off the first switch, wherein the first, second and third semiconductor switches (SW1, SW2, SW3) are turned off, and to turn on the second switch.