A discriminant function specifying device includes a setting part for calculating a discriminant function by machine learning using a learning input parameter, the discriminant function being for separating a distribution of a genuine similarity from a distribution of impostor similarity, the learning input parameter being set before executing the machine learning, and for setting a plurality of discriminant functions, each of the plurality of discriminant functions being obtained by changing values of the learning input parameter and a learning output parameter, the learning output parameter being a parameter of the calculated discriminant function; a calculation part for calculating an error rate for each of the plurality of discriminant functions set by the setting part; and an extraction part for extracting one discriminant function among the plurality of discriminant functions, the one discriminant function having the error rate calculated by the calculation part which meets a predetermined error condition.