Tsugaru-Juniko Lakes consist of the well-known Lake Ao-ike and other 32 lakes in Aomori Prefecture's Tsugaru Quasi-National Park, in the westernmost part of the Shirakami Mountains which has been registered as a World Natural Heritage Site. Tsugaru-Juniko Lakes is considered to have been formed by a landslide triggered by an earthquake that occurred about 300 years ago. An identification of the subsurface structure of the landslide is particularly important for an understanding of the origin of lakes ; however, such data is limited. This study investigated the subsurface structure of the landslide near the Ao-ike by using 2D high-resolution electrical resistivity providing the evidence of the formation of landslide-dammed lakes and new information of the geological data. Besides, historical documents were used to investigate the formation age of the lakes.