To provide a corrugated plate made of synthetic resin and its joint structure preventing the infiltration of water caused by a capillary phenomenon and suppressing fouling with dust.

In the corrugated plate 1 made of synthetic resin with crest parts and trough parts alternately and continuously formed, the corrugated shape of a corrugated plate 2 on one side is different from that of a corrugated plate 3 on the other side, and one of slant face parts from the crest parts toward the following trough parts of the corrugated plate 2 on one side is formed in recess shape, for instance. The corrugated plates made of synthetic resin are arranged in parallel, and the corrugated plate 3 on the other side is placed over the corrugated plate 2 on one side and joined.