To provide a backlight for internal irradiation type indicating lamp, capable of enhancing the visibility of a display board by suppressing unevenness of brightness while suppressing power consumption, and an internal irradiation type indicating lamp provided with the backlight.

The backlight 1c of the internal irradiation type indicating lamp 1 adapted to irradiate a sign of a translucent display board 1a (1b) by emitting light to the display board 1a (1b) from the rear comprises a light emitting part 1j having a plurality of LEDs 1h arranged in a ring shape; and a reflecting plate 1k having a reflecting surface 1m opposed to the light emitting part 1j and having substantially the same size as a front view light emitting part 1j, which is disposed on the rear side of the light emitting part 1j. The reflecting surface 1m includes a plurality of annular reflection parts 1n sharing the center as the front view light emitting part 1j and similar to the light emitting part 1j, the reflection parts 1n being disposed while successively shifting the positions backward in the descending order of the similarity thereof, and each reflection part 1n being formed so as to be gradually extended forward so that the light emitted from the light emission part 1j to the reflector 1k disposed in the rear thereof can be reflected forward.