A power device comprising: a connector (CN1, CN2, CN3) detachably connected to a battery (E1, E2, E3); a power supply unit provided between the connector (CN1, CN2, CN3) and external equipment (G, L) to supply electric power to the external equipment (G, L) ; a switch unit (SA1, SA2, SA3, SB1, SB2, SB3) provided to change over between power supply and power cut-off states unidirectionally from the connector (CN1, CN2, CN3) to the power supply unit ; a connector-side voltage detector configured to detect a voltage of the connector side of the switch unit (SA1, SA2, SA3, SB1, SB2, SB3); a power supply unit-side voltage detector configured to detect a power supply unit-side voltage of the switch unit (SA1, SA2, SA3, SB1, SB2, SB3); a connection determiner configured to determine whether or not the battery (E1, E2, E3) is connected to the connector (CN1, CN2, CN3) on the basis of the connector side voltage detected by the connector-side voltage detector ; and a switch controller configured to control the switch unit (SA1, SA2, SA3, SB1, SB2, SB3) such that electric power is supplied unidirectionally from the connector (CN1, CN2, CN3) to the power supply unit when the connection determiner determines that the battery (E1, E2, E3) is connected; characterized in that , when the connection determiner determines that the battery (E1, E2, E3) is connected, the switch controller determines whether or not the connector-side voltage detected by the connector-side voltage detector and the power supply unit-side voltage detected by the power supply unit-side voltage detector satisfy a predetermined first relationship, and controls the switch unit (SA1, SA2, SA3, SB1, SB2, SB3) such that electric power is supplied unidirectionally from the connector (CN1, CN2, CN3) to the power supply unit depending on a result of the determination. a connector (CN1, CN2, CN3) detachably connected to a battery (E1, E2, E3); a power supply unit provided between the connector (CN1, CN2, CN3) and external equipment (G, L) to supply electric power to the external equipment (G, L) ; a switch unit (SA1, SA2, SA3, SB1, SB2, SB3) provided to change over between power supply and power cut-off states unidirectionally from the connector (CN1, CN2, CN3) to the power supply unit ; a connector-side voltage detector configured to detect a voltage of the connector side of the switch unit (SA1, SA2, SA3, SB1, SB2, SB3); a power supply unit-side voltage detector configured to detect a power supply unit-side voltage of the switch unit (SA1, SA2, SA3, SB1, SB2, SB3); a connection determiner configured to determine whether or not the battery (E1, E2, E3) is connected to the connector (CN1, CN2, CN3) on the basis of the connector side voltage detected by the connector-side voltage detector ; and a switch controller configured to control the switch unit (SA1, SA2, SA3, SB1, SB2, SB3) such that electric power is supplied unidirectionally from the connector (CN1, CN2, CN3) to the power supply unit when the connection determiner determines that the battery (E1, E2, E3) is connected; characterized in that , when the connection determiner determines that the battery (E1, E2, E3) is connected, the switch controller determines whether or not the connector-side voltage detected by the connector-side voltage detector and the power supply unit-side voltage detected by the power supply unit-side voltage detector satisfy a predetermined first relationship, and controls the switch unit (SA1, SA2, SA3, SB1, SB2, SB3) such that electric power is supplied unidirectionally from the connector (CN1, CN2, CN3) to the power supply unit depending on a result of the determination. <EOS>