The Japanese Murrelet Synthliboramphus wumizusume breeds in the Japanese islands. Murrelets have been observed around their breeding islands only during the breeding season. Their distribution and ecology during the non-breeding season are not known because the birds are not seen outside the breeding season. I confirmed the presence of several juveniles and adults in the western Seto Inland Sea. There are no previous records of Japanese Murrelets in this area, as the habitat was thought to be unsuitable. The current study provided the first observations of groups of juveniles and the first observation of adults outside the breeding season. The western part of the Seto Inland Sea was therefore confirmed as the habitat of non-breeding Japanese Murrelets. The observations provide information on the ecology and foraging habitat of the Japanese Murrelet during the non-breeding season. This should be valuable when considering ways of conserving the species.