PURPOSE: To make it possible to more positively carry out the display of the clogging state of the filter by making the end surface forming a light outlet end of an optical fiber an enlarged end surface.

CONSTITUTION: A light outlet side end 19b of a light inlet side optical fiber 19 is opposed to a light inlet end 20a of a display side optical fiber 20 by holding therebetween an operating member 15 which moves when the pressure of a suction side air tunnel 10 positioned between an air filter 5 and a fan 7, among the suction side air tunnel 10 and a blow-off side air tunnel 11. Furthermore, the end surface of a light outlet side end 20b of a display side optical fiber 20 is made into an enlarged end surface, and the enlarged end surface is positioned on the indoor side surface of the air conditioner 1. That is, in order to detect the clogging state of the air filter, no electric power is required, and hence it serves to save energy. Further, when the air filter is clogged, light is irradiated from the light outlet side end 20b to brighten a large area so that the clogging state can be positively informed.