A classical technique relying on thermodynamics is used, and spin sj, which is a variable, is made to follow a local effective magnetic field Bj to bring a system to a ground state of a problem-setting system. The ground state is a solution thereof. At t=0, the effective magnetic field Bj is applied rightward in all the sites, and all the spins sj are initialized rightward. The magnetic field in the z axis direction and the interaction between spins are gradually applied with time t, which finally brings the spins in the +z direction or the −z direction, and the z components of the spins sj become sjz=+1 or −1. In addition, correction parameters originating from quantum mechanical effects are introduced when the direction of the spin sj is made to follow the direction of the effective magnetic field Bj so as to improve calculation performance.