1. An optimal solution search method wherein candidates for solution to a problem are represented as chromosomes which are arrangements of genes and genetic operations are performed for individual chromosomes for each generation to successively update the generation to search for an optimal solution to the problem based on fitness values calculated from gene arrangements of the chromosomes, the optimal solution search method comprising: the fitness value updating step of updating, for each of those chromosomes for which a particular genetic operation which allows a fitness value after execution thereof to be calculated readily making use of a fitness value before the execution thereof, the fitness value based on variation information of the fitness value by execution of the particular genetic operation.