Group-level self-regulation significantly impacts online collaborative learning performance (Panadero & Järvelä, 2015). Recently, online collaborative learning has been actively implemented in English language education in Japan, and group-level self-regulation, closely related to online collaborative learning, attracts the attention of Japanese researchers. However, no instrument has been developed to measure group-level self-regulation. Therefore, this study aims to adapt the Group Metacognition Scale (GMS) developed by Biasutti and Frate (2018) to Japanese and test it with a sample of eTandem English learners in Japan. Then, a comparison of self-directed and teacher-directed learning was made using GMS to determine whether they differ in their three metacognitive processes: planning, monitoring, and evaluating. The results showed that the Japanese version of the GMS comprised 18 items consistent with the four factors of the original version and had good internal consistency. This suggests that the Japanese version of the GMS is a valid and reliable tool for research and practice with Japanese-speaking populations. In addition, a comparison of mean scores for metacognitive processes revealed that the group metacognitive skills required for self-directed learning could be improved.