engine valve operating system having side walls 22 and 23 ensures the following advantages the attracting force characteristic of the electromagnet 7 shown by the curve a in fig4 is ensured by the magnetic circuit shown by a in fig5 by installing side walls 22 and 23 of soft magnetic material at side surfaces of the plate type electromagnet 7 having an e shaped cross section a new magnetic circuit of magnetic flux is generated as shown by arrows b in fig5 when a distance between electromagnet 7 8 and movable plate 15 is greater than a first predetermined distance the magnetic circuit shown by the arrow b circulates in the order of the inner magnetic pole of electromagnet 7 air gap a lower surface of movable plate 15 a side surface of the movable plate 15 side wall 22 or 23 and the outer side of electromagnet 7 the reason for generating the new magnetic circuit b is that when the distance between movable plate 15 and electromagnet 7 is relatively large the magnetic resistance of the magnetic circuit b becomes smaller than that of the magnetic circuit a on the other hand when movable plate 15 sufficiently approaches electromagnet 7 the magnetic resistance of the magnetic circuit a becomes smaller than a second predetermined distance therefore when the air gap between movable plate 15 and electromagnet is zero or sufficiently small the magnetic circuit a generates the.