To provide an attachment for honing mounted on a working machine to effect working through rotation of a main spindle, and capable of exerting rotation and axial vibration on a tool for working, and being compact and solid.

The attachment is mounted on a working machine having a rotary main spindle, transmits rotation of the main spindle to a tool for working, and exerts axial vibration on a tool. The attachment comprises an offset joint to bring rotation, inputted from the working side to a disc on the input side, into an eccentric state by a link to effect crank motion; an eccentric amount adjusting device to adjust an eccentric amount of the offset joint; a hook joint formed that an end part on the drive side is coupled to the disc on the output side of the offset joint; and an output shaft coupled to the end part on the driven side of the hook joint. The output shaft is rotatably and vertically movably supported and a mounting part for tool is situated at an end part on the opposite side to the hook joint.