Guide numbers tgn1, tgn2 as expected light amounts of a main flashlight and a remote flashlight are added for the calculation of an expected illumination amount of each divided photometric region. If there is an over-illuminated region, among the divided photometric regions, in which the expected illumination amount exceeds a proper illumination amount for a subject, the guide numbers tgn1 and tgn2 are decreased such that of the two flashlights, the one illuminating the over-illuminated region more is given a larger decrease. In this manner, guide numbers gn1, gn2 for main flash of the main flashlight and the remote flashlight are calculated so as to adjust the expected illumination amount of the over-illuminated region to a proper value.