It is possible to enhance accuracy in photometry measurements without an increase in unnecessary actual measurement data and design value data in the case where on a low ambient luminance side, an output of a first light sensor, which receives light collected from a large area, is linear and an output of a second light sensor, which receives light collected from a small area, is non-linear. The number of luminance measurement points used for performing measurement with the second light sensor is set at low ambient luminance values to be larger than the number of luminance measurement points used for performing measurements with the first light sensor. Accordingly, it is possible to enhance accuracy of photometry measurements without an increase in unnecessary actual measurement data and design value data where an output of a brightness detecting circuit based on an output of the second light sensor is non-linear and an output of a brightness detecting circuit based on an output of the first light sensor is linear.