The present invention relates to a fuel cell system capable of controlling a temperature using a fluid. The fuel cell system includes: a fuel cell module generating power by a chemical reaction; first circulation flow part connected to an entrance and exit of the fuel cell module to circulate a first fluid controlling reaction heat of the fuel cell module; a second circulation flow part in which a hydrogen storage unit for supplying hydrogen into the fuel cell module is disposed, the second circulation flow part circulating a second fluid controlling a temperature of the hydrogen storage part unit; a heat exchanger connected to the first and second circulation flow parts to allow heat of the first and second fluids to be exchanged; and a control part controlling a flow rate of each of the first and second fluids introduced into the heat exchanger on the basis of a power value generated by the fuel cell module so that the reaction heat of the fuel cell module and the temperature of the hydrogen storage part are controlled.
