PURPOSE: To reduce the trouble of attachment by a method wherein an insertion member is attached with a support member provided on a predetermined position.

CONSTITUTION: Even if a mark showing an attachment position is not provided, the attachment position of the insertion member 4 can be fixed by attaching the insertion member 4 to a support member 3 which is a predetermined position. As the support member 3 and the insertion member 4 are coupled with each other with the respective coupling parts 32d and 41b, the positioning can be performed easily although the operation by which the insertion member 4 is attached to the support member is a relatively difficult screwing operation. As a notch 41c is provided in the insertion member 4 near an attachment part 41a and a wide space is provided, by positioning a driver in that space, it is not necessary to take an unnatural posture and the operation can be performed easily. With this constitution, the trouble of the attachment can be reduced.