A warming device for fuel cell system having a fuel battery and a secondary battery has a first heater, a second heater and a control device. The first heater heats the secondary battery. The second heater heats the fuel battery by using electricity of the secondary battery. In warming of the fuel cell system, the control device first drives the first heater to heat the secondary battery to a preset temperature, and then drives the second heater. This reduces warming time of the fuel cell system.