1. An image pickup system comprising: noise estimating means comprising: parameter calculating means for calculating parameters of a function using the signal value level of digitized signals from an image pickup element in which a plurality of pixels are arranged, and at least one type of information selected from, the temperature of the image pickup element, the gain for the signals and the shutter speed during shooting; noise amount calculating means for calculating an amount of noise (N) contained in the signals, for one of each pixel and each specified area comprising a plurality of pixels responsive to the parameters calculated by the parameter calculating means; and noise reducing means for reducing the noise contained in the signals on the basis of the amount of noise calculated by the noise calculating means.