When obtaining a final result from a discriminator group arranged in a predetermined order, an evaluation value obtaining unit successively evaluates each discriminator from a first discriminator and if it is determined that a discrimination result represented by an overall evaluation value obtained by evaluating the first to Ith discriminators remains unchanged even if evaluation values of I+1th and subsequent discriminators are added to the overall evaluation value, a discrimination result determination unit instructs the evaluation value obtaining unit to terminate the evaluation of the I+1th and subsequent discriminators, and determines the discrimination result according to the overall evaluation value obtained by evaluating the first to Ith discriminators as a final result.