PURPOSE: To carry through operations safely and surely by providing a working truck with a stepped member possible to swing oscillatingly, and by arranging so that action of one of them can be stopped while the other is in service.

CONSTITUTION: A tool has its working surface possible to change freely so as to be capable of carrying through various works with different surfaces to be processed with the aid of a link mechanism etc. On a working truck 2 is placed a stepped member 3, at whose sides 4, 5 gate-shaped stays 6, 7 are installed upright to horizontal swingable support, a hanging member 8 at which a tool retainer 9 is hung movably in the vertical direction. The stepped member has its bottom surface formed in an arc of circle and can swing oscillatingly. Between the truck 2 and this stepped member 3 is installed a stopper rod 123 which can be rotated by a lever 127, and at this rod are installed a plate 131 to hinder the truck from moving and a detent member 134 to hinder the stepped member 3 from swinging while they are grounded alternately through the rotation of the rod in such an arrangement as working one after the other.