To simplify a chuck holder by fixing a chuck head to one tip of a chuck head holder in a radial direction by a circular member the chuck head holder guides by a base and adjusting its position by driving the holder to simplify the holding of a grinding head.

The chuck head 1 is provided with a chuck 2 holding an instrument to be ground, and the chuck head 1 to fix to the circular chuck head holder 3 and the grinding head 4 including a grinding wheel 5 are pivotally attached to a rotary plate 6. The chuck head holder 3 is rotatable upward at 30° and downward at 45°, e.g. from a horizontal position. In addition, the head 1 can decide various positions with respect to the holder 3 around its center shaft at 20° in each direction at the time of its maximum rotation by a snap means in the form of the ball of a spring elastic pressure, e.g. This rotating movement is required for grinding the surface of some instrument and a further different position and rotating angle can be required by another device.