Abstract: An electronic component embedded substrate includes an electronic component and a heat transfer block which are embedded in insulating layers, a first wiring patterns facing a first surface of the heat transfer block, a second wiring pattern facing a second surface of the heat transfer block, a first via conductor connecting the first wiring pattern and the first surface of the heat transfer block, and a second via conductor connecting the second wiring pattern and the second surface of the heat transfer block. The first and second surfaces and are insulated from each other. Thus, even when an electronic component of a type having large heat generation and being prohibited from connecting to a ground pattern is mounted, the second wiring pattern functioning as a heat dissipation pattern can be connected to a ground pattern on a motherboard.