Opinion dynamics is a complex collective behavior in human societies. When individuals exchange opinions with others, they usually adopt a bounded confidence rule and only accept the opinions within the confidence range. Furthermore, individuals are heterogeneous in real social systems. Thus, they have distinct confidence levels, and also play different roles in the collective opinion formation. In this paper, a leader-follower bounded confidence model is proposed for a group of social agents, who have heterogeneous confidence levels, at the same time, come from two subgroups: opinion leaders and opinion followers. Simulation results are obtained for the collective opinion evolution influenced by three factors: the leader fraction, the group size and the trust degree. The results show that the roles of opinion leaders are remarkable when the opinion followers have high confidence levels and trust degrees.