Abstract: A first storage unit holds the values of discrete variables included in an evaluation function and the values of local fields for each replica. A second storage unit provided for each replica holds the values of corresponding discrete variables and local fields. A processing unit repeats, for each replica, a process of updating the value of any discrete variable, the value of the evaluation function, and the values of the local fields on the basis of a set temperature and the values of the local fields stored in the second storage unit, and after every predetermined number of iterations, performs resampling of population annealing. When a first replica is duplicated to create a second replica, the processing unit reads the values of the discrete variables and local fields of the first replica from the first storage unit and stores them in the second storage unit for the second replica.