A fuel cell apparatus is formed by connecting four stacks via a supply/discharge box. A cooling water supply opening and a cooling water discharge opening are short-circuited by a cable so as to eliminate the electric potential difference therebetween. To avoid hindrance of gas flow due to water droplets, a drain port for discharging water droplets is provided near a fuel gas discharge opening of the supply/discharge box. Each stack is formed by clamping end plates disposed on opposite ends of stacked cells through the use of upper and lower tension plates. The thus-formed fuel cell apparatus is housed in an outer case that has a sealed construction for preventing penetration of foreign substances. Thus, the apparatus achieves a size reduction and an improvement in practicality.