To provide an inexpensive and high-grade roof plate member for ordinary house by providing a plurality of rib parts on the rear surface of a flat part having such plate thickness that holds strength as the roof plate member formed by aluminum extrusion molding.

The plurality of rib parts 13 are provided at a fixed interval in parallel in the longitudinal direction on the rear surface of the flat part 11 provided with an eaves side connection part 20 by bending an eaves side end downward and a ridge side connection part 30 by bending the eaves side end upward and are integrally extrusion-molded. A top part of the rib part may be flat or an arclike part.