An exposure control unit comprising a photometer, a designator, a first calculator, a first counter, a selector, a second calculator, a categorizer, and an exposure controller is provided. The photometer comprises a plurality of photometric zones. The designator designates the photometric zones one by one as a target zone. The first calculator calculates a first difference. The first counter counts a first determination number. The selector selects the target zone of which the first determination number is greater than a second threshold. The second calculator calculates a categorization value. The categorizer categorizes a target zone into low- or high-luminous zones. The exposure controller controls an exposure of the imaging apparatus on the basis of the partial value of light for one of the low- and high-luminous zones.