A DC-DC converter module includes a multi-layer substrate, a switching IC, and a coil. The multi-layer substrate includes component mounting electrodes provided on the top surface and an input terminal, an output terminal, and ground terminals provided on the bottom surface. The switching IC switches an input voltage and includes an input electrode, an output electrode, and a ground electrode, and is mounted on the top surface of the substrate by connecting the electrodes to the component mounting electrodes. The coil is arranged within the multi-layer substrate in a spiral shape with an axis extending in the substrate stacking direction. The bottom surface side end of the coil is connected to the input/output electrode of the switching IC.