An on-vehicle oil sensor includes an enclosure and a detecting unit. The enclosure includes: an enclosure inner space provided inside the enclosure and configured to allow oil to enter the enclosure inner space; and a plurality of oil paths provided in the enclosure and connecting an exterior of the enclosure to the enclosure inner space. The detecting unit is configured to detect at least one of pressure of oil in the enclosure inner space and temperature of oil in the enclosure inner space.