The present study examined effects of positive emotions toward task activities that arise from interactions with another person, in a collaborative construction process of knowledge, using error bias as an index of this process. Third-graders performed a sequence of tasks : a pre-test, a collaborative session, and a post-test. The experimenter responded differently to participants' reactions in 2 different conditions : surface-acceptance and deep acceptance. The hypothesis that only the participants in the latter condition would experience positive emotions was confirmed. The participants in the deep-acceptance condition showed more error biases, performed the post-test tasks more properly, and were more flexible about rethinking their original idea through employing different ideas from others. The present findings suggest that positive emotions toward task activities prompt children involved in a task to be more flexible toward others' ideas, thus allowing them to rethink their original idea from a new perspective.