PURPOSE: To reduce weight in an automobile door by fixing an inner panel by joining an outer panel, a flange coming into contact with the peripheral inside surface, the rise part, an inner installing part, a middle panel, a mask part of a central opening part and a rise part and the like together integrally.

CONSTITUTION: An outer panel 2 composed of a cold rolling steel plate forms a hemming part 2a in a peripheral part. A middle panel composed of an aliminium material forms a flange 3a inscribed in the hemming part 2a, a rise part 3b continuing to this flange part 3a and an inner installing part 3c, and a nut 5 is welded to the reverse side of the inner installing part 3c, that is, to the side facing the outer panel 2. An inner panel 6 forms an installing flange 6a and a mask part 6c, and the inner installing part 3c is butted by the installing flange 6a by sandwiching a juction 7 to hold an impact bar 8 between them, and a bolt 4 is screw-fitted/fixed to the nut 5. Since there is no limitation caused by a controversial point of a raw material in welding, a lightweight material can be used.