1. An imaging apparatus comprising: a reference mark determination section ( 203 ) which determines an area in which a reference mark is present, from a shot image obtained by shooting a stage ( 13 ) on which the reference marks of known shapes are repeatedly laid out at predetermined intervals, and an original ( 5 ) placed on the stage ( 13 ); a count section ( 203 ) which sets a check area ( 82 ) to the shot image, and determines the number of pixels of an area in which the reference mark determined by the reference mark determination section ( 203 ) is present, in the check area ( 82 ); an area determination section ( 203 ) which compares the number of pixels determined by the count section ( 203 ) with a predetermined first numeric range, and determines that the check area ( 82 ) is an area occupied by the stage ( 13 ) if the number of pixels is within the first numeric range; and an acquisition section ( 203 ) which determines a boundary between the stage ( 13 ) and the original ( 5 ) based on a determination result of the area determination section ( 203 ), and acquires an area in which the original ( 5 ) is present.