R, G and B signals are output from individual pixels provided at an image-capturing element. Pixel output averages corresponding to the R, G and B signals are calculated for each of partition areas into which the light-receiving surface of the image-capturing element is divided. Ratios of the R and B pixel output averages to the G pixel output average are calculated for each partition area. Then, any area with the ratios of the pixel output averages within a predetermined range is extracted from the plurality of partition areas. R and B white balance gains are calculated based upon the total sums of the pixel output averages corresponding to the individual colors in the extracted area. A white balance adjustment is then executed by multiplying the values of R and B pixel outputs by the corresponding white balance gains.