To suppress pulsation in a rotating situation of a spindle drive while continuously rotating a workpiece for finish-machining in the spindle drive of a machine tool.

In the spindle drive of a machine tool comprising; a rotating body including a spindle rotatably supported by a frame body and a rotationally driven member fixed on the end of the spindle; and a drive for driving the rotating body, the braking device comprises: a braking member including an elastically deformable braking part, the braking member being mounted on the frame body or on the rotating body; a pressing force applying device for applying pressing force to the braking member by a working fluid; and a braking face mounted on the frame body side: wherein the braking part deflects under pressing force and goes into a situation in which the braking face and the rotating body-side sliding face facing the braking face are pressed each other, thereby applying rotating resistance to the rotating body to be able to rotate; and further a low-frictional coefficient member is fixed on either the braking face or the sliding face of the brake part.