Semiconductor light source lighting circuit

A semiconductor light source lighting circuit comprising:

• a switching regulator that generates a drive current of a semiconductor light source using a switching element;
• and
• a control circuit that controls ON/OFF of the switching element so that the drive current approximates to a target value,
• wherein the control circuit comprises:
• a comparator that compares the drive current and the target value;
• an up/down counter that counts a digital value in a count direction determined by a comparison result of the comparator;
• a digital-analog converter that converts the digital value counted by the up/down counter into an analog signal;
• and
• a drive circuit that controls the ON/OFF of the switching element based on the analog signal which is obtained as a result of the conversion by the digital-analog converter, and
• wherein the up/down counter counts said digital value at a speed determined by an ON/OFF cycle of the switching element.