This study clarifies how network structures in multiplex networks affect the emerging cooperative behavior among individuals. For this purpose, we conduct experiments of prisoner's dilemma on multiplex networks that are composed of two layers. Each layer is selected from three networks: a random network, small-world network, and scale-free network. We find that cooperative behavior emerges only in the multiplex network composed of two scale-free networks. Furthermore, individuals of a hub who have a cooperative strategy play an important role.