A bandwidth extension apparatus can generate from an inputted speech signal a bandwidth-extended signal whose bandwidth is automatically adjusted according to the surrounding hearing situation by means of a parameter. The apparatus has a surrounding characteristic predictor for predicting the characteristic amount of the surrounding sound of the phone terminal on which the apparatus is installed; an adjustment amount predictor for comparing the characteristic amount with the parameter to predict the adjustment amount for the parameter; a speech characteristic predictor for predicting the characteristic amount of the inputted speech signal; and an adjustment amount determiner for determining an adjustment amount for updating the parameter based on the characteristic amount of the surrounding sound and the inputted speech signal.