To provide a rotating machining device capable of cutting or grinding under a load according to various needs, and suppressing problems caused by increase in size and complication.

A grinding device 1 is provided with a main shaft 2 of a machining center, an air motor 3 provided rotatably independent from the main shaft 2, and a grinding wheel 5 provided at the tip end of a rotating shaft 4 of the air motor 3. An outer cylinder 8 is interposed between the main shaft 2 and the air motor 3, and a pressing force adjusting mechanism is provided in the outer cylinder 8. When carrying out grinding machining under a specified load, the main shaft 2 is rotated, and a rotating pan 16 is rotated along with the rotation of the main shaft 2. An movable pan 21 coupled through an upper link 23 and a lower link 25 is rotated. When a rotational speed of the main shaft 2 is increased, a centrifugal force acts on a weight 26, and the movable pan 21 and a press element 18 are forced to move in the direction separating from the main shaft 2, so that the force of the air motor 3 moving downward against the energizing force of a coil spring 28 is increased.