A semiconductor light-emitting element lighting device comprising: a switching element serially connected to a DC power source; a control circuit (1, 2) for turning on/off the switching element at high frequency; an inductive element to which a current is intermittently passed from the DC power source via the switching element; a rectifying element for passing the current flowing from the inductive element; a smoothing capacitor charged with the current flowing from the inductive element via the rectifying element; and an impedance element (R1, R2) connected to the smoothing capacitor in parallel, the lighting device driving a semiconductor light-emitting element by a voltage between both ends of the impedance element (R1, R2), wherein: the control circuit (1, 2) comprises means adapted to make an on-duty of the switching element variable; and a value of the impedance element (R1, R2) is set so that a current flowing to the semiconductor light-emitting element is larger than a current flowing to the impedance element (R1, R2) when the on-duty of the switching element is maximum and the current flowing to the impedance element (R1, R2) is larger than the current flowing to the semiconductor light-emitting element when the on-duty of the switching element is minimum, characterized in that the means adapted to make the on-duty of the switching element variable is provided by means adapted to make both the ON period and the ON/OFF frequency of the switching element variable. a switching element serially connected to a DC power source; a control circuit (1, 2) for turning on/off the switching element at high frequency; an inductive element to which a current is intermittently passed from the DC power source via the switching element; a rectifying element for passing the current flowing from the inductive element; a smoothing capacitor charged with the current flowing from the inductive element via the rectifying element; and an impedance element (R1, R2) connected to the smoothing capacitor in parallel, the lighting device driving a semiconductor light-emitting element by a voltage between both ends of the impedance element (R1, R2), wherein: the control circuit (1, 2) comprises means adapted to make an on-duty of the switching element variable; and a value of the impedance element (R1, R2) is set so that a current flowing to the semiconductor light-emitting element is larger than a current flowing to the impedance element (R1, R2) when the on-duty of the switching element is maximum and the current flowing to the impedance element (R1, R2) is larger than the current flowing to the semiconductor light-emitting element when the on-duty of the switching element is minimum, characterized in that the means adapted to make the on-duty of the switching element variable is provided by means adapted to make both the ON period and the ON/OFF frequency of the switching element variable. the control circuit (1, 2) comprises means adapted to make an on-duty of the switching element variable; and a value of the impedance element (R1, R2) is set so that a current flowing to the semiconductor light-emitting element is larger than a current flowing to the impedance element (R1, R2) when the on-duty of the switching element is maximum and the current flowing to the impedance element (R1, R2) is larger than the current flowing to the semiconductor light-emitting element when the on-duty of the switching element is minimum, characterized in that the means adapted to make the on-duty of the switching element variable is provided by means adapted to make both the ON period and the ON/OFF frequency of the switching element variable.