In the current Japanese EFL context, the promotion of communicative competence has been highly recommended, and hence the importance of task based language teaching or the use of output activities is focused heavily on due to its possibility to enhance not only language proficiency and use but also learners' motivation to learn English and willingness to communicate. However, there has been not so much research investigating the effects of open tasks on the development of communication variables. This study attempts to reveal whether or not learners' communication variables would change through a seven-week long debate project. The results indicated that from a global perspective learners' trait and state willingness to communicate and communication apprehension did not significantly vary whereas their trait and state perceived communication competence significantly developed. This study also discovered that from an individual perspective the debate was more effective for those who were less oriented toward communication. It ends with some pedagogical and future implications.