This paper analyzes Japanese students' communication activities in group work with international students in English in a task-based Intercultural Communication course, and examines its educational effectiveness, based on their self-evaluation. It then suggests how we can motivate Japanese students to participate in intercultural communication courses and improve their intercultural communication competence. This course was conducted at a graduate school of science, so the students' majors may not necessitate an immediate need of their intercultural communication skills. Therefore, the main objective of the Japanese students taking this course was to improve their English communication skills rather than promote their interests in intercultural issues. This desire motivated the Japanese students to participate in group work and communicate with international students in English. They completed their task, which was to translate information about the university's campus from Japanese into English, in cooperation with international students, while experiencing differences in communication style, and difficulties in making themselves understood in English. As a result, they learned how to carry out communication in a foreign language with students of different languages and cultural backgrounds, by using a number of different strategies, such as non-verbal communication, and asking other students to act as translators. Moreover, the accomplishment of the task gave the students confidence in interacting with international students in English, and encouraged them to communicate more with international students in English. It was concluded that these achievements were brought about by their strong motivation to develop their English communication skills, and the task activity, which promoted the students'communication in the group.