An FC system disclosed herein may comprise a plurality of FC units, a cooler, and a controller. Each of the FC units may comprise a FC stack, a supply passage/a return passage/a circulating passage through which refrigerant passes, and first temperature sensor. The supply passage supplies the refrigerant from the cooler to the FC stack. The return passage returns the refrigerant to the cooler. The circulating passage is connected to the supply passage and the return passage. The first temperature sensor is configured to measure a temperature of the refrigerant in the supply passage at a position upstream of a merging point of the supply passage and the circulating passage. When measured values of the first temperature sensors of the plurality of the FC units do not match, the controller is configured to provide notification about malfunction of the first temperature sensor.