A feature extracting unit extracts a feature vector of an input speech. A similarity calculating unit calculates degrees of similarity for each of a plurality of noise environments, based on the feature vector. A compensation-vector calculating unit acquires a first compensation vector from a storing unit, calculates a second compensation vector based on the first compensation vector, and calculates a third compensation vector by weighting and summing the second compensation vector with the degree of similarity as weights. A compensating unit compensates the feature vector based on the third compensation vector.