There are provided a retaining unit that retains a basic model indicating a plurality of relations for a plurality of subject conditions between a plurality of illuminances and a plurality of luminance of a plurality of captured images, which are obtained when a subject is imaged by changing an illuminance condition under the subject conditions; a reference image acquiring unit that acquires a captured image captured in a target space for illuminance estimation as a reference image; a reference illuminance acquiring unit that acquires illuminance of the target space at a time of imaging the reference image as reference illuminance; and an illuminance estimation model generating unit that generates an illuminance estimation model indicating a relation between illuminance and luminance in the target space from a data value indicated as a pair of the reference illuminance and luminance of the reference image based on the basic model.