First support portions 71 and 72 positioned on a predetermined straight line L2 approximately perpendicular to a broken line of a hinge portion is set in a support portion 70 that supports a back plate 27 with respect to a back face side of a door portion 36. Second and third support portions 73 and 74 positioned in line symmetry with respect to the straight line L2, are set in the support portion 70. It is possible to receive the centrifugal force, which is applied to the back plate 27 due to the expansion of the door portion 36, with good balance by the first to third support portions 71, 72, 73, and 74. An emblem 24 can be reliably fixed to the door portion 36 with preventing a fixing pin 31 from being excessively locked into a through hole 33 more than necessary.