A circuit for lighting a semiconductor light source is provided. The circuit includes: a switching regulator including a switching element and configured to generate a drive current for the semiconductor light source using the switching element; and a control circuit configured to control on-off of the switching element such that the magnitude of the drive current comes close to a targeted value. The control circuit includes: a comparator configured to compare the magnitude of the drive current with the targeted value; an up/down counter configured to count a digital value in a counting-up direction or counting-down direction, based on a comparison result of the comparator; a digital-to-analog converter configured to convert the counted digital value into an analog signal; and a drive circuit configured to control on/off of the switching element based on the analog signal.