DESCRIZIONE
A gear mounting structure (20, 220) includes a worm shaft (21, 221), a gear (123, 223, 323), and an elastic member (24, 224). The worm shaft (21, 221) includes a shaft body (25), on the outer surface of which is formed intersecting spiral grooves (25a), and a gear locking portion (126, 226, 326) with a non-circular cross section, on at least a portion of the outer surface of which is formed a curved surface portion (26a, 226a) and a planar portion (26b, 226b). The gear (123, 223, 323) includes a gear body (28), on the outer surface of which are formed teeth, and to which the handle rotation is transmitted, and a boss portion (30, 130, 230, 330) protruding from the gear body (28) and having an engagement portion (30a, 230a) engaging the gear locking portion (26, 126, 226, 326). The elastic member (24, 224) is mounted so as to abut the outer surface of the boss portion (30, 130, 230, 330) of the gear (23, 123, 223, 323), and at least a portion of the curved surface portion (26a, 226a) of the gear locking portion (26, 126, 226, 326). [Image Omitted]