Gas flow channels are provided between protrusions arranged in parallel on a first surface of a partition wall of a gas flow channel forming body, and water introduction channels are provided in valleys on the opposite side of each protrusion, on a second surface. In order to allow the gas flow channels and the water introduction channels to communicate so that water can pass there through, communication channels is provided to the partition wall. Intermediate structures are correspondingly provided inside the water introduction channels to the communication channels. A set of communication channels is formed by a pair of communication channels positioned at a first interval. A set of communication channels and another set of communication channels adjacent thereto are positioned on each protrusion with a second interval therebetween.