Patent ID: 8736990

Claim:
An attachment structure configured to attach a first member to a second member by relatively rotating the first member and the second member in a circumferential direction about a predetermined axis, comprising: a first engagement portion which is provided at one of the first member or the second member and which protrudes in a radial direction with respect to the axis as a center; and a second engagement portion which is provided at the other one of the first member or the second member and which engages with the first engagement portion at least at a predetermined attachment position in the circumferential direction to restrict a relative movement of the first member and the second member in a direction of the axis, wherein one of the first member or the second member at which the second engagement portion is provided, is provided with spaces which allow the first engagement portion to pass by the second engagement portion in the direction of the axis, at both sides of the second engagement portion in the circumferential direction, and the first member and the second member include a torque change portion which changes a torque during the relative rotation between the first member and the second member so that the torque is larger at a preceding side and a succeeding side of the attachment position in the circumferential direction, than at the attachment position.