PURPOSE: To realize the optimal white balance of the color signals of negative pictures by adjusting the color signals so that the maximum levels of the three kinds of the color signals can be coincident with each other, and the minimum levels of the three kinds of the color signals can be coincident with each other.

CONSTITUTION: Three primary color signals G, R, and B indicating picked-up object images are outputted from an image pickup device 10. A peak detection circuit 12 detects both the maximum level and the minimum level of input signals, and the maximum level and the minimum level correspond to a black peak level and a white peak level, respectively. A microcomputer 11 controls variable gain amplifying circuits 15 and 16 by using input data indicating the black and white peak levels in order to adjust the white balance. Moreover, the black and white peak levels, and tonal characteristics of the color signals G, R, and B are made coincident with each other by γ correcting circuits 41, 43, and 45.