To provide a tool floating mechanism capable of detecting the abnormality in an attitude change of a rotary driving source from an origin attitude.

In the tool floating mechanism, a flange 72 of the rotary driving source 50 is biased to be held between a flange abutment part 27F and a movable ring 25 provided in a support sleeve 13, and normally the rotary driving source 50 is held in the origin attitude. Then, when a rotary tool 52 receives a load laterally to change the attitude of the rotary driving source 50, the movable ring 25 moves away from the flange abutment part 27F following tilting of the flange 72 to operate a limit switch 31. Here, even when the rotary driving source 50 tilts in any direction from the origin attitude, the movable ring 25 uniformly moves away from the flange abutment part 27F following tilting of the flange 72. Thus, abnormality concerning loads from all lateral directions to the rotary tool 52 is detected only by one limit switch 31.