To provide a charger capable of stably charging a battery regardless of a solar radiation state.

A charger 1 comprises: a solar panel 10; a step-down converter 110; a control CPU 111; a step-down converter 12; and a vehicle control device 13. An input terminal and output terminal of the step-down converter 110 are connected to an output terminal of the solar panel 10 and an auxiliary battery BL, respectively. An input terminal and output terminal of the step-down converter 12 are connected to a main battery BH and the auxiliary battery BL, respectively. The control CPU 111 performs MPPT control of the step-down converter 110 so that output power of the solar panel 10 is maximum. The vehicle control device 13 performs constant voltage control of the step-down converter 12 so that output voltage is a predetermined voltage value. The step-down converter 12 can perform constant voltage charging of the auxiliary battery BL. Thereby, the auxiliary battery BL can be stably charged regardless of a solar radiation state.