A seat cushion extension apparatus comprises a slide rail disposed on a lower side of a cushion frame; an extension panel coupled to a front end of the slide rail and disposed on a front side of the cushion frame; an extension motor having a lead screw, disposed on the lower side of the cushion frame; a first hinge bracket coupled to the end of the slide rail and disposed at a rear upper side of the extension panel; and a second hinge bracket coupled to the end of the lead screw and disposed at a rear lower side of the extension panel, wherein the extension panel is configured to slide forward along the slide rail and to extend forward while rotating in a front upper direction through actuation of the lead screw driven by the extension motor.