An illumination apparatus of the present invention quickly adjusts illuminance of the light radiated from the light source in the irradiation surface to have high uniformity. The illumination apparatus includes the light source that emits a light beam having a rectangular shape, a DMD on which light emitted from the light source is incident and which controls reflection/non-reflection of the incident light by opening/closing control of minute mirrors, an optical system that shapes the light reflected by the DMD, a half mirror that splits the light emitted from the optical system into irradiation light and monitor light, the irradiation surface irradiated with the irradiation light, a monitor unit that measures illuminance of the monitor light, and a control unit that transmits a control signal to control opening/closing of the minute mirrors of the DMD to the DMD, based on a measurement result measured by the monitor unit. In this case, an illuminance distribution in the irradiation surface is adjusted to a predetermined value.