The present invention controls the pressure and flow rate of fluid, in order to obtain uniform performance, configure a closed loop magnetic circuit so as to include an electromagnet, a flapper, and a yoke material, and elastically deform the flapper itself by Maxwell attractive force generated between a magnetic pole of the electromagnet and the flapper to make the separation distance between the nozzle and the flapper variable. As opposed to a rigid flapper structure that swingably moves around a supporting point, like a conventional servo valve, the electromagnet, the magnetic pole, the nozzle, the flapper, and the like are arranged such that a change in magnetic gap directly leads to a change in air gap.