Voltage signals outputted from a CCD are subjected to correlated double sampling processing by a correlated double sampling circuit (CDS), after which digital gain processing is carried out at a gain control amplifier (GCA). A gain difference between G color signals and R/B color signals outputted from the CCD is caused by a difference between a G exposure duration t.sub.G and an R/B exposure duration t.sub.R/B. When the value of a ratio between the t.sub.G and the t.sub.R/B falls below a predetermined value, the GCA applies digital gain for compensating for the gain difference by multiplying respective signal values of R, G and B by gain correction coefficients as follows: (gain compensation coefficient .alpha.)=(G exposure duration t.sub.G)/(R/B exposure duration t.sub.R/B)=(G exposure duration t.sub.G)/((G exposure duration t.sub.G)+(exposure duration difference .DELTA.t)).