An electric circuit used in a vehicle having an idling stop function of automatically stopping and automatically restarting an engine, the electric circuit comprising: an electric generator (2, 60); a lead storage battery capable of charging and discharging electric power generated by the electric generator (2, 60); a non-aqueous electrolyte secondary battery connected in parallel to the lead storage battery, capable of charging and discharging the generated electric power, and having high durability against repetitive charge and discharge compared to the lead storage battery; and engine restart means (9,60) connected to the lead storage battery and the non-aqueous electrolyte secondary battery, and cranking the engine at a time of the automatic restart; switching means connected between the engine restart means (9,60) and the lead storage battery, and capable of blocking a flow of current between the engine restart means (9,60) and the lead storage battery; wherein the switching means comprises at least a first relay; wherein at the time of the automatic restart, the switching means blocks the flow of current between the engine restart means (9,60) and the lead storage battery, and the engine restart means (9,60) is driven by the electric power supplied from the non-aqueous electrolyte secondary battery, characterized in that the switching means further comprises a semiconductor switch, in addition to the first relay, wherein the semiconductor switch is connected in parallel to the first relay; and wherein the semiconductor switch includes a parasitic diode, which is connected in such a manner that a forward direction of the parasitic diode matches a direction from the non-aqueous electrolyte secondary battery toward the lead storage battery, and wherein the semiconductor switch is closed and the first relay is opened when the engine has been automatically stopped, and the semiconductor switch is opened at the time of the automatic restart. an electric generator (2, 60); a lead storage battery capable of charging and discharging electric power generated by the electric generator (2, 60); a non-aqueous electrolyte secondary battery connected in parallel to the lead storage battery, capable of charging and discharging the generated electric power, and having high durability against repetitive charge and discharge compared to the lead storage battery; and engine restart means (9,60) connected to the lead storage battery and the non-aqueous electrolyte secondary battery, and cranking the engine at a time of the automatic restart; switching means connected between the engine restart means (9,60) and the lead storage battery, and capable of blocking a flow of current between the engine restart means (9,60) and the lead storage battery; wherein the switching means comprises at least a first relay; wherein at the time of the automatic restart, the switching means blocks the flow of current between the engine restart means (9,60) and the lead storage battery, and the engine restart means (9,60) is driven by the electric power supplied from the non-aqueous electrolyte secondary battery, characterized in that the switching means further comprises a semiconductor switch, in addition to the first relay, wherein the semiconductor switch is connected in parallel to the first relay; and wherein the semiconductor switch includes a parasitic diode, which is connected in such a manner that a forward direction of the parasitic diode matches a direction from the non-aqueous electrolyte secondary battery toward the lead storage battery, and wherein the semiconductor switch is closed and the first relay is opened when the engine has been automatically stopped, and the semiconductor switch is opened at the time of the automatic restart.