A temperature detection unit (14a) detects the temperature of a power plug (14). A control unit (20a) stops electric conduction to a battery (6) when the detected temperature detected by the temperature detection unit (14a) is equal to or higher than a predetermined specified temperature (T1). The control unit (20a) recovers the electric conduction to the battery (6) when the detected temperature detected by the temperature detection unit (14a) decreases to a specified temperature (T2) or lower, the specified temperature (T2) being lower than the specified temperature (T1).
