An ambrosia beetle, Platypus quercivorus, is the vector of Japanese oak wilt, one of the most serious forest diseases in Japan. P. quercivorus is widely distributed in the main islands of Honshu, Kyushu and Shikoku, but there have been no records of P. quercivorus in Hokkaido, the northernmost main island in Japan. Because the mass mortality of oak trees caused by Japanese oak wilt is spreading northward in northern Honshu, we sampled P. quercivorus in 20 forest sites in the southernmost part of Hokkaido by using pheromone traps. Five P. quercivorus (two males and three females) were collected from four sites. Because oak species distributed in Hokkaido are all susceptible to Japanese oak wilt, monitoring and control measures will be needed to prevent the spread of Japanese oak wilt in Hokkaido.