To provide a grinder, grinding while reducing the influence of abrasion of a grinding wheel.

This grinder includes: a support rotatably supporting a cylinder A having a circumferential surface; the grinding wheel 3 for grinding the circumferential surface while the cylinder A is rotated; an electric motor 4 for driving the grinding wheel 3 in rotation; a moving means for moving the support 1 in the direction of intersecting the center line of rotation of the grinding wheel 3; a means for setting the peripheral speed ratio of the grinding wheel 3 to the cylinder A; and a control part for controlling the rotating speed of the grinding wheel 3 on the basis of the peripheral speed ratio set by the means, wherein the peripheral speed ratio of the grinding wheel 3 to the cylinder A during grinding is set to the uniform peripheral speed ratio.