A method of producing a skin-covered pad for a seat, which includes (a) preparing a lower mold which has a cavity formed therein, the lower mold having a first electrode mounted thereto through an insulator, the first electrode having a plurality of projections which are exposed to the cavity; (b) putting a bag-shaped outer skin member into the cavity, the skin member being thermally plastic; (c) putting an upper mold on the lower mold to close the cavity, the upper mold having an aperture formed therethrough; (d) projecting a press member into the cavity through the aperture, the press member having at its work head a second electrode secured thereto through an insulator, the second electrode having at its front face recesses which are shaped to match with the projections of the first electrode; (e) pressing the recessed face of the second electrode against the projections of the first electrode with a part of the outer skin member therebetween; (f) applying a high frequency current between the first and second electrodes thereby to heat and thus soften the part of the outer skin member; (g) separating the recessed face of the second electrode from the projections of the first electrode; and (h) pouring a liquid material for foamed plastic into the cavity and curing the same.