A first control circuit is configured to detect a value of a load current flowing through a solid-state light source in a lighting time period, and control a control element at a first response speed so as to make the value of the load current agree with a first target value. A second control circuit is configured to detect the value of the load current in the lighting time period, and control the control element at a second response speed so that the value of the load current does not exceed an upper limit that is larger than a first target value. The second response speed is higher than the first response speed.