Abstract: An end plate of a fuel cell stack is directly fixed to a humidifier. A resin pipe is attached to an oxygen-containing gas outlet of an end plate through a resin coupling pipe. The resin pipe includes one end having a large diameter and the other end having a small diameter. The other end is provided at an off gas supply channel of the humidifier. The off gas supply channel includes an inclined channel. The other end extends up to an end of the inclined channel where inclination of the inclined channel is started. An off gas ejection port is formed at the other end. The off gas ejection port is opened to the end of the inclined channel where inclination is started. Condensed water returned along the inclined channel flows from the off gas ejection port into the resin pipe.

Abstract: An apparatus includes a gas sensor configured to detect a specific gas which is a subject for detection, and inspection gas introduction piping configured to lead an inspection gas to the gas sensor, wherein at least a portion of the inspection gas introduction piping serves as ventilating piping configured to ventilate an inside of a ventilation-requiring device.