a method for heating and press - forming a plied material sheet prepared by impregnating a thermosetting resin into sheets of parallely disposed plastic fiber or into sheets of woven fabric of plastic fiber . the material sheet is formed into an operation which repeats the steps of heating and press - forming such material sheet within a shaping mold on a heating and press - forming apparatus for a predetermined time period and then releasing the pressure for a predetermined time period while step - feeding the material sheet over a predetermined distance for a time period less than the time period of such released pressure .