Provided is a battery-charging device that uses a full-bridge rectifier circuit in which each arm is composed of MOSFET as a circuit that rectifies an output of a magnet-type AC generator. The charging device comprises: an ON/OFF state establishment means that, on the basis of a polarity of a potential of each input terminal of the rectifier circuit, establishes ON/OFF state to be assumed by each MOSFET of the rectifier circuit when a battery is charged; a during-charging FET control means that performs control which matches the state of each MOSFET of the rectifier circuit with the state established by the ON/OFF state establishment means when the battery is charged; a short-circuit control means that performs short-circuit control which causes short-circuiting between output terminals of the generator when battery charging is paused; and a FET OFF means that generates a FET OFF time period in which all of the MOSFETs of the rectifier circuit assume an OFF state in a fixed cycle. While short-circuit control is being performed as well, information for establishing the states to be assumed by the MOSFETs of the rectifier circuit during battery charging can be obtained during the FET OFF time periods.