A pin assembly includes: a resin pin; and a collar fitted to a round shaft portion of the resin pin and having higher hardness than the resin pin. The round shaft portion is sheared to cancel connection between a first plate and a second plate upon secondary collision of a vehicle. The collar includes an end face received by a reception surface of the second plate, and shears the round shaft portion in a shear plane along the end face upon the secondary collision. The round shaft portion includes a hollow hole. An inner circumference of the hollow hole includes a straight portion which has a generating line parallel to an axial direction of the round shaft portion and which is traversed by a plane including the end face of the collar.
