A seat belt-integrated vehicle seat is provided with an improved seat frame rigidity, without a size precision decrease of the entire seat frame. The vehicle seat with a seat belt includes a seat back frame having at least a pair of side frames, and an upper frame for coupling a pair of the side frames on the upper side, a shoulder anchor portion provided in an upper part of the side frame, the shoulder anchor portion into which a shoulder belt portion of the seat belt is inserted, and a reclining device provided in a lower part of the side frame, in which the side frame has a closed section structure portion having a hollow closed section, and an extension portion integrally formed by downwardly extending a surface of the closed section structure portion and positioned on the outer side, and the reclining device is attached to the extension portion.