To inexpensively provide an illumination apparatus applicable to an existing ceiling cassette type air conditioner, and a ceiling cassette type air conditioner composed integrally with the illumination apparatus.

The illumination apparatus 12 is for the ceiling cassette type air conditioner 10 including an air conditioner body 14 installed in a space above the ceiling, and a rectangular decorative panel 16 exposed to a ceiling surface. The illumination apparatus includes corner panels 22 attached to corner parts 40 of the decorative panel 16, luminaires 26 installed in openings 24 formed in the corner panels 22, and a power supply unit 28.