To facilitate the maintenance such as mounting and replacement of a light emitting unit using LEDs.

A lamp 3 integrally having a light emitting unit 5 and a transformer 7 is mounted on the lamp box 1 of a signal lamp in such a manner as to be attachable and detachable. The light emitting unit 5 has two or more LEDs 11 aligned on a board 10 to form a light emitting surface for displaying a signal. The transformer 7 is provided on the power source circuit of the light emitting unit 5 for preventing the pseudo lighting of LEDs. In the maintenance, inspection or replacement of the light emitting unit 5, it is taken out from the lamp box 1 together with the lamp 3 including the transformer 7, or it is mounted within the lamp box 1 to eliminate the wiring connection between the light emitting unit 5 and the transformer 7.