An apparatus and method for controlling auto exposure (AE) that is used in digital imaging devices. The apparatus controlling the luminance of an image being outputted from an image sensor by controlling exposure time and analog gain of the image sensor includes: a luminance operation unit operating and outputting a mean luminance of the image outputted from the image sensor; a shutter index determination unit comparing a predetermined target luminance with the mean luminance of the outputted image and determining a shutter index in different manners according to the magnitude of the difference between the target luminance and the mean luminance of the outputted image; and an exposure time/analog gain determination unit generating exposure time and analog gain corresponding to the shutter index determined in the shutter index determination unit and applying the generated exposure time and analog gain to the image sensor.