A solid light-emitting element lighting device comprising: a direct-current power source, and a series circuit of an inductor and a switching element that are connected between output terminals of the direct-current power source via a load; a diode for regenerating, during turning-off of the switching element energy accumulated during turning-on of the switching element in the inductor to the load; and a control circuit part for controlling on and off of the switching element, wherein the control circuit part includes a drive signal generation part for generating a drive signal whose pulse width varies in accordance with an amplitude of a load current (Il), and controls the on and off of the switching element according to the drive signal in an on-period or an off-period of a PWM signal whose on-duty varies in accordance with a dimming level, the PWM signal being a lower frequency than the drive signal; and a voltage detection part for detecting the load voltage applied to the load and feeding back the load voltage to the direct-current power source is provided; characterized in that the direct-current power source includes an AC-DC converter or a DC-DC converter to which the detected load voltage is fed back and that controls the output voltage (Vout) to be K times larger than the detected load voltage according to Vout = K × V 1, and that the direct-current power source is adapted to set the output voltage (Vout) to be larger than the load voltage and to be 2.5 times as large as the load voltage or less according to 1 < K ≤ 2.5; wherein the the on-duty (Don) of the switching element is Don = V 1 Vout a direct-current power source, and a series circuit of an inductor and a switching element that are connected between output terminals of the direct-current power source via a load; a diode for regenerating, during turning-off of the switching element energy accumulated during turning-on of the switching element in the inductor to the load; and a control circuit part for controlling on and off of the switching element, wherein the control circuit part includes a drive signal generation part for generating a drive signal whose pulse width varies in accordance with an amplitude of a load current (Il), and controls the on and off of the switching element according to the drive signal in an on-period or an off-period of a PWM signal whose on-duty varies in accordance with a dimming level, the PWM signal being a lower frequency than the drive signal; and a voltage detection part for detecting the load voltage applied to the load and feeding back the load voltage to the direct-current power source is provided; characterized in that the direct-current power source includes an AC-DC converter or a DC-DC converter to which the detected load voltage is fed back and that controls the output voltage (Vout) to be K times larger than the detected load voltage according to Vout = K × V 1, and that the direct-current power source is adapted to set the output voltage (Vout) to be larger than the load voltage and to be 2.5 times as large as the load voltage or less according to 1 < K ≤ 2.5; wherein the the on-duty (Don) of the switching element is Don = V 1 Vout