PURPOSE: To provide the honing device the grinding wheel expanding mechanism of which is simplified.

CONSTITUTION: The slide sections 5b of a plurality of grinding wheel mounting pieces 5 are slidably provided for the tip end section of rotating shaft 4 rotatably supported by a cylindrical main body 2 so as to be freely expanded/ contracted, a grinding wheel 6 is mounted at the tip end sections of the grinding wheel mounting pieces 5, each expanding weight 7 is concurrently mounted on a base end section, and a return spring 8 is wound around the circumference of the intermediate sections of the grinding wheel mounting pieces 5. Besides, the grinding wheel mounting pieces may be made slidable along a guide cylinder in place of the slide sections 5b, so that the aforesaid mounting pieces are expanded/contracted by means of fluid led into a fluid chamber.