A feed screw mechanism includes a feed screw shaft connected to a drive source and formed with first screw threads on an outer circumferential surface thereof, and a displacement nut, which is screw-engaged with respect to the feed screw shaft through a plurality of balls. The displacement nut is supported with respect to a slider that makes up an electric actuator by a pair of pins. The pins are inserted and fixed in first pin holes formed in the slider, and distal end portions of the pins are inserted respectively into second pin holes formed in the displacement nut.