Provided is a fuel cell system (FCS) which acquires an operation state of the fuel cell (FC) and estimates the IV characteristic which shows the relationship between current and voltage in the fuel cell (FC). The fuel cell system (FCS) obtains at least one of the resistance overvoltage, the activation overvoltage, the current/voltage hysteresis, and the concentration overvoltage from the operation state of the fuel cell (FC) and estimates the IV characteristic in accordance with the obtained result.