A converter is provided in which the cost and size of which are reduced by a decrease in current consumption with no need of large elements or radiation fins. The converter has a switching element (Q1) being connected to a DC power source through a primary winding (P) of a transformer (T), a control circuit (4) for turning on/off the switching element (Q1), a diode (D51) and a capacitor (C51) for rectifying/smoothing the voltage induced in the secondary winding (S) of the transformer (T) to extract DC output, and a starting circuit (5) for starting the control circuit (4). The starting circuit (5) operates as a constant current circuit (Q2, R1, R2, ZD1, D1) while starting the control circuit (4), and as a constant voltage circuit (Q2, R1, R2, ZD2, D1) after starting the control circuits (4).