A representative pattern memory stores a plurality of initial representative patterns as a noise pattern. Different attribute is affixed to each initial representative pattern. A pitch pattern memory stores a large number of natural pitch patterns as an accent phrase. A clustering unit classifies each natural pitch pattern to the initial representative pattern based on the attribute of the accent phrase. A transformation parameter generation unit calculates an error between a transformed representative pattern and each natural pitch pattern classified to the initial representative pattern. A representative pattern generation unit calculates an evaluation function of the sum of the error between the transformed-representative pattern and each natural pitch pattern classified to the initial representative pattern, and updates each initial representative pattern. The representative pattern memory stores each updated representative pattern as a clustered pattern of the attribute affixed to the corresponding initial representative pattern.