To provide a device for dressing a polishing pad which suppresses generation of scratches when polishing.

This device is pressed on the polishing pad 4 to dress the polishing pad 4, while rotating a diamond disc 7. The diamond disc 7 is manufactured by fixing many diamond particles 9 to the surface of a base metal 8. In a polygon obtained by performing two-dimension projection of each of the diamond particles 9, an average value of a diagonal line ratio defined as a value that the length of the longest diagonal line of a plurality of diagonal lines of the polygon of the same particle is divided by the length of the shortest diagonal line is within a range of 1.17 to 1.23.