To suppress deterioration of vibration during a rotary operation time by no-load of a grinding wheel without disturbing a vibration reduction effect during a grinding work.

A rotary tool includes a grinding wheel 1, a center hole 2a provided in a substrate 2 of the grinding wheel 1, a lock nut 20 including a boss section 21 to be inserted into the center hole 2a, a wheel washer 6 holding the substrate 2 together with the lock nut 20, and an annular elastic body 5 interposed between the substrate 2 and the wheel washer 6. An annular adapter 30 is integrally provided around the center hole 2a and is slidable in a shaft direction of the boss section 21. The lock nut 20 and the annular adapter 30 are brought into close contact with each other in tapered surfaces 23 and 33, and force in a direction reducing eccentricity of the center hole 2a in relation to a screw hole of the lock nut 20 is applied by elastic force of the elastic body 5.