The present invention is characterized by repeatedly AD converting in a time series an output of each light sensitive element, and at the same time an added value or a mean value of each one of said AD converted values is obtained so that such added value or a mean value is used as an output of each light sensitive element. According to the present invention, an influence of flickering of an artificial light source can be eliminated and at the same time a light measuring computation with a high level of accuracy can be made with a higher speed than that in a conventional method, and particularly in a light measuring apparatus housing a number of light sensitive elements a light measuring computation with a high level of accuracy can be made in a by far faster speed than that in a conventional method.