To provide a detection device of light source state capable of displaying a light-control state of a lamp (a light source) and whether an unlit state of the lamp is due to its life, in a simple structure.

A lighting state display device 110 is provided with a plurality of LEDs, a lamp detection circuit 90 for detecting whether a discharge lamp 42 is mounted, a lamp-end-of-life/non-lighting detection circuit 95 for detecting whether the discharge lamp 42 is at end of life, and whether it is a non-lit lamp, a microcomputer 80 for detecting a light-control state of the discharge lamp, whether the discharge lamp is mounted or not, whether the discharge lamp is at end of life, and whether the discharge lamp is an unlit lamp, as a state of the discharge lamp, and making the LEDs emit light in accordance with the detected state, and optical fibers f1 to f4 inputted with light emitted by the LEDs and guiding the inputted light to output it.