Vehicular / closing device

A vehicular / closing device (11) has: a support member (10) having a telescopic shaft shape, between a body (4) and a door (3) of a vehicle (1) is disposed, and which thereby is capable of to keep the door in an open position, wherein the support member comprises a cylindrical casing that houses a driving source (23), and a joining element (40, 40a, 40b) which is fixed, with a portion thereof of the corresponding in one end portion the housing is inserted, and that is attached to the body or the door of the vehicle, and wherein the joining element has a contact portion that comes to the housing in contact when the joint member is attached to the housing, and on which convex portions (45a) and concave portions (45b) which are recessed with respect to the convex portions in a radial direction toward an inner side, are alternately provided in a circumferential direction.