PURPOSE: To remove a chattering phenomenon of a work at its cutting, by attracting a work with an electromagnet mounted onto a work supporting bed of a working machine and clamping the work further through a clamping mechanism.

CONSTITUTION: A side clamping device is provided to a bed (8). This side clamping device is constituted such that a side clamp (10) securing an electromagnet (9) on the bed (8) and a side clamp (12) securing an electromagnet (11) are placed at a face-to-face position, and a nut (13) secured to a bottom part of the clamp (10) is screwed to a screw rod (15) rotated by a handle (14) in front of the bed while the clamp (12) is connected to a piston rod (18) of an oil hydraulic cylinder (17) mounted to the bed (8) further the clamp (12) is longitudinally moved by the cylinder (17) with respect to the clamp (10) adjusting its set position by the handle (14). Then a work 16 at its cutting is not displaced in the direction of the clamps 10, 12 also in the reverse direction, that is, the internal displacement is also inhibited by work attractive force of the electromagnets 9, 11, to never cause the displacement, and chattering is not generated in a work clamped place, then suppressive action of this chattering is effected to the neighboring place of the clamp.