GRINDER

PROBLEM TO BE SOLVED: To provide a grinder capable of grinding and polishing the peripheral surface of a material to be ground by a simple constitution with high accuracy. SOLUTION: With the grinder 1, a rotating grinding wheel body 13 of a grinding unit 5 reciprocating along the axis of rotation of a rotating material to be ground, is pressed against the peripheral surface of the material to be ground to grind it. A grinding wheel body-rotary shaft 15 connected to the rotary grinding wheel body 13 independently of a motor-driving shaft 50, is connected to the motor-driving shaft 50 of a motor 12 for driving the rotating grinding wheel body through a ball spline mechanism 48 so that the grinding wheel body-rotary shaft can advance to or retract from the material G to be ground. Then, a pressing force adjusting means 120 which is made up of a first cylinder connected to the motor-driving shaft 50 side, a first piston body 57 connected to the grinding wheel body-rotary shaft 15 side to slide in the first cylinder 58, and a first gas supplying means 63 for supplying compressed air and the like into the first cylinder 58, and which drives the first piston body 57 by compressed air and the like sent from the first gas supplying means 63 to adjust pressing force of the grinding wheel body 13 to the material G to be ground, is provided.