1. A parameter tuning device for tuning a large number of parameters in a physical model of a semi-conductor device, comprising: parameter tuning means for defining chromosomes having a plurality of respective parameters of the physical model for performing simulation of the semiconductor device as a gene and optimizing the plurality of parameters of said physical model using a genetic algorithm based on characteristic measurement data of a test-manufactured semiconductor device, and said parameter tuning means including a child chromosome generating means, said child chromosome generating means obtaining a center of gravity of a parent chromosome group in a vector space selected in a crossover process in the genetic algorithm; determining a hyper-polyhedron on a vector space shown by a peak of vectors which extend to each selected parent chromosome from said center of gravity and are respectively multiplied by predetermined times; and generating a child individual using a uniformly distributed random number so as to be housed inside said hyper-polyhedron and be used in a simulation of a LSI manufacture on an LSI processing line using physical models of transistors.