Abstract: Non-linear outputs x.sup.A and x.sup.B for input signals x are calculated by referring to look-up tables, in which pairs of input and output signals with respect to gamma coefficients A and B different from each other are stored. These outputs x.sup.A and x.sup.B are multiplied by coefficients (1-k) and k, respectively, and the products are added to each other. Gamma correction outputs are approximately outputted from the result x.sup.A .times.(1-k)+x.sup.B .times.k. Any desired gamma characteristics can be obtained by varying the value of k in the range of 0 to 1. It is sufficient that the gamma characteristics data stored in the look-up tables (in advance) are only two kinds of data. A variety of gamma characteristics can be provided without increasing the memory capacities of the look-up tables.