PURPOSE: To prevent an operation lever from dropping with certainty by fitting an elastic leg around a shaft hole of the operation lever, and forming a fitting groove being in sliding contact with an outer side surface thereof.

CONSTITUTION: An installation part 21 of an operation lever 20 is positioned and pushed into an upper portion of a support shaft 12 of a base 10. An elastic leg 13 is thus widened outward, and a shaft hole 22 of the operation lever 20 is fitted to a fitting projection 11 of the support shaft 12. At the same time, an engagement claw 14 is engaged with an edge of a fitting groove 23, and the operation lever 20 is rotatably supported by the support shaft 12. When the operation lever 20 is rotated, an escape preventive projection 15 of the elastic leg 13 is in sliding contact with an inner side surface of the fitting groove 23, preventing the elastic leg from being widened outward. The engagement claw 14 does not escape from the edge of the installation part 21, and the operation lever 20 is not dropped from the support shaft 12. In order to demount the operation lever 20, the lever 20 is operated, and its cutout 24 is positioned to a cutout stepped portion 17 of a rib 16. Afterward, the elastic leg 13 is widened outward. Thus, an engagement claw 3 can be separated from the edge of the operation lever 20.