Abstract: A battery charger includes: a circuit board including terminal portions provided to be exposed to the outside from an insertion portion, in which a secondary battery is inserted, and electrically connected to the secondary battery; a power circuit portion obtaining a voltage from an external power source and supplying a charging current to the secondary battery; a temperature detection unit detecting a battery temperature of the secondary battery; a charging control switch turning on/off the charging current; and a controller controlling the power circuit portion or the charging control switch based on a voltage and a current of the power circuit portion and the battery temperature, wherein the temperature detection unit is provided in a part of the circuit board opposed to the insertion portion at a distance from electronic components constituting the power circuit portion and the controller based on a heat generation temperature of the electronic components.