Disclosed is a joining structure for joining dissimilar materials, such as a plastic plate and a metal plate. The joining structure is positioned or formed at where a plastic plate and a metal plate are joined. The joining structure includes: a self-piercing rivet piercing through the plastic plate to be pressed onto the metal plate and subjected to plastic deformation. In particular, the plastic plate includes a self-healing capsule containing a self-healing agent in a base material of a plastic resin and a catalyst being polymerized with the self-healing agent. The self-healing capsule is broken by a crack of the base material at a periphery of a pierced portion of the plastic plate, and the self-healing agent flowing out of the self-healing capsule fills a gap of the crack and causes polymerization with the catalyst to cure the crack portion.