1. A proportion predicting system for predicting elements to be mixed and their proportions to realize a given target, said system comprising: a target characteristic extractor for extracting a characteristic of the predetermined target; an evaluating means operable upon receipt of proportion vectors, which are represented by the characteristic of the predetermined target and the quantity of each of the elements, respectively, to determine fitnesses of the proportion vectors based on the extracted characteristic of the predetermined target; and a GA processor for predicting the proportion vectors on the basis of the fitnesses according to a genetic algorithm in which the quantity of each of the elements and each of the proportion vectors are represented by a gene and a chromosome, respectively; said proportion vectors, which have been predicted by the GA processor, being inputted to the evaluating means to cause said evaluating means to repeat evaluation of the proportion vectors to determine optimum proportion vectors.