A memory unit stores maps of predetermined determination threshold values for detection values detected by a hydrogen sensor according to an operating state of a fuel cell such as a difference in pressure between reaction gases at an anode and a cathode, supply pressure of the reaction gases, supply flow rate of the reaction gases and generated current of the fuel cell. A control unit obtains a predetermined determination threshold value from the memory unit based on the operating state of the fuel cell. Then, the detection value outputted from the hydrogen sensor and the determination threshold value obtained from the memory unit are compared, and in the event that the detection value is determined to exceed the determination threshold value, a predetermined protecting process is implemented for the fuel cell.