To uniformly polish a wafer with high accuracy by placing a contact part between a dresser and a polishing pad on a straight line.

A dresser 17 is formed by arranging many ring-like teeth 19 for dressing where diamond is electro-deposited side by side on the surface of a cylinder 18 as a base. The cylindrical dresser 17 is disposed horizontally in such a manner that with the axis of the cylinder 18 parallel to the surface of a polishing pad 1, the bus of the cylinder side is brought into straight-line contact with the surface of the polishing pad 1 at the time of dressing. By the rotation of the cylinder 18, the teeth 19 where diamond is electro-deposited are rotated to dress the polishing pad 1. The length of the cylinder 18 of the dresser 17 is made larger than the diameter of a wafer 3 to uniformalize wafer polishing. At the time of dressing, the cylindrical dresser 17 is arranged rectilinearly in the radial direction of the polishing pad 1. Accordingly, the contact pat between the polishing pad 1 and the diamond teeth 19 of the dresser 17 is such that plural contact points are arranged rectilinearly.