A variable impedance circuit (2) has an impedance device and is connected in series with a light source (A1). A switch circuit (Q1) is connected in parallel with the variable impedance circuit (2). A first controller (3) is configured to perform ON and OFF control of the switch circuit (Q1) and thereby to modulate an intensity of an illumination light emitted from the light source (A1). An impedance-varying circuit (Q2) is connected with the variable impedance circuit (2). The second controller (4) is configured to control the impedance-varying circuit (Q2) to change the impedance of the variable impedance circuit (2). The first controller (3) and the second controller (4) share a common hardware.