PURPOSE: To make the fine adjustment of location, requiring the extent of high precision, achievable without being affected by size of a measuring instrument by setting the connecting position of a connecting member connecting a turning lever and a decelerating lever down to a position where a turning radius of the turning lever becomes larger than that of the decelerating lever.

CONSTITUTION: When each free end of decelerating levers 13a-13d is turned round with a first fulcrum shaft 12a as the center, each connecting part of these decelerating levers is displaced. At this time, the connecting position of a connecting member 16 connecting these turning and decelerating levers is set down to a position where a turning radius of the turning lever 6 becomes larger than that of the decelerating lever, a connecting part of the decelerating lever is displaced to be smaller than that of each free end of the decelerating levers through the principles of the lever and fulcrum. Simultaneously with this, displacement in this connecting position has the connecting part of the turning lever displaced as much as the same value via the connecting member, thereby rotating the turning lever with a second fulcrum shaft 12b as the center.