PURPOSE: To prevent the depression, abrasion, etc., of the collar receiving part of a main plate in the falling of a winding step and switching operation by securing the contacting area of the collar part positioned on a timepiece base frame above a specific value.

CONSTITUTION: The collar 8 of the winding stem 1 is expanded within a permissible range at a maximum in terms of the function of the timepiece, the clearance between the winding stem bearing diameter (d) of the main plate and the collar diameter D of the winding stem is suppressed without any trouble to the switching operation, and a slanting surface C1 for returning the winding stem 1 is suppressed small within a workable range. Further, the degree determining part of the main plate is stepped down by one sectionally to store the collar 8, so a flash C2' of the main plate is not formed at the contacting part with the collar 8 in terms of work, so that the need for a slanting surface for preventing the formation of the flash is eliminated. The contacting area of the collar 8 is secured above 0.15mm2 by the structural operation. Consequently, the breakage of components such as depression is prevented against impact force and compressive force during the falling.