A mountable electronic circuit module which produces appropriate characteristics without a complicated structure can be a DC-DC converter including a baseboard made of a magnetic material. A helical electrode is provided in the baseboard so as to function as a smoothing inductor device. Capacitor devices in addition to a DC-DC converter IC are mounted on a main surface of the baseboard. A circuit electrode arranged to connect the circuit devices is provided to enable the circuit devices to function as the DC-DC converter. The DC-DC converter is mounted on a motherboard through external connection electrodes of the capacitor devices.