An apparatus and method for automatically producing door panels in a single line in order to enable continuous production are provided. In the apparatus, a first uncoiler supplies the wound inner plate material. A first leveler regulates a flatness of the inner plate material. A press forms a pattern on the inner plate material. A marking device marks a cutting position on the inner plate material from the presser. A bend controller controls a bend of the inner plate material from the marking device. A second uncoiler supplies an outer plate material. A second leveler regulates a flatness of the outer plate material supplied from the second uncoiler. A roll forming device roll-forms both edges of the inner and outer plate materials. A heater preheats the inner and the outer plate materials. An injector injects insulated material between the inner and outer plate materials. A marking sensor senses the mark on the inner plate material and outputs a sensing signal. A cutter cuts the door panel at a fixed size according to the sensing signal. According to the apparatus, the inner and outer plate materials are processed while continuously passing through each device so that the door panel is completed.