A photometer comprising a measurement button and a FIX key; a photoelectric conversion circuit which is actuated by the measurement button so as to start a measurement; a random-access memory which holds a measured light value, obtained through the measurement by the photoelectric conversion circuit, when the FIX key is operated; an accumulator which calculates deviation of a measured light value obtained through the measurement effected by the photoelectric conversion circuit from the measured light value held by the random-access memory; and a display element by which; (a) when the random-access memory is not holding a measured light value, a measured light value obtained through the measurement effected by the photoelectric conversion circuit is displayed, (b) when the random-access memory is holding a measured light value and the measurement button is out of operation, the measured light value being held is displayed, and (c) when the random-access memory is holding a measured light value and the measurement button is operated, the deviation obtained by the accumulator is displayed instead of the measured light values while the measurement button is in operation.