PURPOSE: To provide a coarse and fine adjustment device capable of making fine adjustment strictly by obtaining drive members fixed completely to a main device ranging from a coarse adjustment knob to a speed reducing mechanism when a fine adjustment knob is operated rotatably.

CONSTITUTION: An annular internal gear 31 is mounted concentrically on an output shaft 41 provided in series with a coarse adjustment knob 11, and an elliptic cam 33 rotated integrally with a fine adjustment knob 12 is provided inside the internal gear 31. An outer teeth 35a held rotatably relative to each other on the outer periphery of the elliptic cam 33 and deflected according to the rotational displacement of the elliptic major axis of the elliptic cam 33 to correspond with the elliptic major axis is provided with a flexible gear 35 meshed with internal teeth 31b of the internal gear 31 at two positions. Then an engaging gear part 13a and a movable engaging part 15a as an engaging mechanism of mesh type which stop and release of rotation of the coarse adjustment knob 11 are provided between the coarse adjustment knob 11 and a main device 10.