PURPOSE: To suppress leakage flux and improve a productivity by a method wherein a fixed-board side coil and a movable-board side coil, which surround a fixed die and a movable die respectively, are provided in an area surrounded by tie-bars of a die tightening device.

CONSTITUTION: A fixed board 10 and a die tightening cylinder 12 are connected by four tie-bars 14 and a die tightening piston 16, coupled with the cylinder 12, is guided by the tie-bars 14 and connected to a movable board 18 which is movable along the axial direction. A movable-board side coil 28, which surrounds a movable die 22, is supported for a movable-die fitting plate 20 by a slide-guide 30 and on the other hand a fixed-board side coil 32, which surrounds a fixed die 26, is supported for a fixed-die fitting plate 24 by a slide-guide 34. Each one of the slide-guides 30, 34 has rollers 31, 35 which are provided perpendicular to each other and provided to each corner of the fitting boards 20, 24. With this constitution, leakage flux can be suppressed and a productivity can be improved.