PURPOSE: To permit a workpiece mount to be rapidly moved according to the working dimension of a workpiece in a machine for working the side of a plate-like body such as a jig or the like by moving back and forth the workpiece mount in interlocking relation with an opposed slide bed.

CONSTITUTION: A workpiece mount 3 and working tool opposed to and interlocked with a slide bed 1 are simultaneously moved by moving the slide bed 1 back and forth and adjusting the interval between both mount 3 and bed 1 according to the working dimension of a workpiece 17. Also, when a locating guide interlocked with the slide bed 1 is provided on at least one side position of the workpiece mount 3, the workpiece 17 will be located only by forcing the side of workpiece 17 against the locating guide and mounting it to span the workpiece mount 3. Further, when a clamp plate 25 is provided on the upper position of a saddle 10, the workpiece 17 is fixed to the workpiece mount 3 by the clamp plate 25 and the slide bed 1 or saddle 10 is reciprocated to work both sides of the workpiece 17.