A built-in illumination apparatus according to the present technology includes a light fixture unit and a light source unit. The light fixture unit includes an outer contour portion to be built in a wall portion including a ceiling, and a first fitting portion. The light source unit includes a light source section, an additional functional section, and a second fitting portion, the light source section emitting light for illumination, the additional functional section having an additional function other than the illumination, the second fitting portion detachably fitting with the first fitting portion, the light source unit being disposed in the outer contour portion by the fitting.