A first LUT composed of table values of brightness of N subjects determined in such a manner that the integrated value is made to be constant and a second LUT composed of table values of N charge storage time periods corresponding to the table values of the brightness of the N subjects are provided. When an image has been picked up with charge storage time at an n-th address in the second LUT, integrated value &Sgr; obtained by the calculating means 6 is divided by the n-th charge storage time S so that the brightness L of the subject is calculated. The charge storage time S corresponding to the calculated brightness L of the subject is selected from the first and second LUT so that exposure is controlled.