To provide a printed wiring circuit board which can be made light in weight and high in mounting density.

The printed wiring circuit board includes a substrate 1 made of a carbon fiber reinforced aluminum alloy containing carbon fibers dispersed into an aluminum alloy matrix, an insulating film 2 provided on one side of the substrate 1, and a conductive film pattern 3 formed on the insulating film 2. Semiconductor elements 4 are mounted on the board. In this case, parts 5 of the substrate 1 on which the semiconductor elements 4 are mounted have a carbon fiber dispersion percentage higher than the other part thereof so that a thermal expansion coefficient of the semiconductor element mounted parts 5 is as low as that of the semiconductor element. Since the substrate 1 is made of a carbon fiber reinforced aluminum alloy, the substrate is light in weight. Further, since the parts of the substrate 1 corresponding to the mounted positions of the semiconductor element 4 have a high carbon fiber dispersion percentage and have a thermal expansion coefficient as low as that of the semiconductor element destruction of the element 4 caused by a thermal expansion difference therebetween can be prevented and high density mounting thereof can be realized.