PURPOSE: To make it possible to obtain the required strength only when it is required by a method wherein a first magnetic circuit is composed of a semi-hardened magnetic member, equipped with an excitation coil, a magnet and a magnetic material to be attracted, a second magnetic circuit is composed of the above-mentioned magnet and a soft magnetical material, an excitation coil is excited by the magnet for a short period in the same direction as the magnetic field, and the attraction force of the material to be attracted is controlled through switching of forces between strong/weak.

CONSTITUTION: A first magnetic circuit A is composed of semi-hardened magnetic bodies 2 and 3, equipped with excitation coils 5 and 6, and a magnet 1 in such a manner that a magnetic body 4 to be attracted will be attracted, and another second magnetic circuit B is composed of a magnet 1 and a soft magnetic soft material 7. In this magnet 1, its magnetic force can be maintained either in strong and weak states even when a current is interrupted. In this knitting machine, a device, with which the mechanism such as stitch cams 22b and 22d, a cam 25 and the like are switched according to the progressing direction of a carriage 21, is constituted by the above-mentioned electromagnet 41, the attraction force of the electromagnet is intensified only when the carriage 21 is inverted, and the attraction force is weakened when the electromagnet is travelling performing a knitting operation, thereby enabling the electromagnet to travel smoothly.