Seal structure and transmission including the same

A seal structure between an oil outlet formed in a first case and an oil inlet formed in a second case and having an end face facing an end face of the oil outlet with a clearance between the end faces, the seal structure comprising:

• an annular first seal disposed in an increased-diameter hole, which is formed on an outlet side or an inlet side of an oil passage in one of the oil outlet and the oil inlet and has a larger diameter than the oil passage, such that the first seal contacts a step surface located at a boundary between the oil passage and the increased-diameter hole;
• and
• an annular second seal harder than the first seal and disposed in the increased-diameter hole such that the second seal contacts the first seal and the end face of the other of the oil outlet and the oil inlet,
• wherein, in an axial direction, the step surface, the first seal, the second seal and the end face of the other of the oil outlet and the oil inlet are arranged in this order such that the step surface first contacts the first seal, the first seal second contacts the second seal and the second seal third contacts the end face of the other of the oil outlet and the oil inlet.