A printed circuit board, having a plurality of via-holes provided in an area where circuit elements are arranged, includes a thermally conductive material having thermally good conductivity, for example copper, and the thermally good conductive material is formed in an inner wall of each of the plurality of via-holes. Each of the plurality of via-holes has, for example, a circular shape, and is arranged in the form of hexagonal or triangular lattice in the area where the circuit elements are arranged. Further, preferably, a diameter of each of the plurality of via-holes is equal to a hole pitch having an allowance .+-.0.3 mm. According to above structure, it is possible to provide a plurality of via-holes per unit area with high density on the printed circuit board and to improve the thermal conductivity of the printed circuit board by effectively radiating the heat generated from the circuit elements.