The purpose of this study is to examine the effects of leader's cognitive structure upon the appropriateness of his role-taking and upon the group-performance. In Experiment I and II two indices were presented: preferred coworkers (DP) and non-preferred coworkers (DN) scores, which represent the variability of leader's cognition, and classified our leaders into 8 types on the basis of the 3 indices; DP, DN, & ASo. Results revealed that high DP-high DN leaders were more effective than the leaders of any other types, and that the group conducted by the leader of the other six types did not differ from each other in their productions.