To provide a polishing device capable of exactly controlling a polishing amount of a material to be processed.

The polishing device for polishing the material to be processed includes: a chuck table for rotatably holding the material to be processed; a spindle having a first through hole at a center; a motor for rotating the spindle; and a polishing pad having a second through-hole communicating with the first through-hole at the center, having a diameter larger than that of the material to be processed and polishing the material to be processed held at the chuck table while covering it, and being mounted at the tip of the spindle. The polishing device includes: a polishing means arranged above the chuck table; a first moving means for relatively moving the chuck table and the polishing means in a vertical direction; a second moving means for relatively moving the chuck table and the polishing means in a horizontal direction; and a noncontact type thickness detection means arranged in the first through-hole of the spindle and detecting the thickness of the material to be processed held at the chuck table through the second through-hole of the polishing pad.