The present invention is a speech synthesizer that generates speech data of text including a fixed part and a variable part, in combination with recorded speech and rule-based synthetic speech. The speech synthesizer is a high-quality one in which recorded speech and synthetic speech are concatenated with the discontinuity of timbres and prosodies not perceived. The speech synthesizer includes: a recorded speech database that previously stores recorded speech data including a recorded fixed part; a rule-based synthesizer that generates rule-based synthetic speech data including a variable part and at least part of the fixed part, from received text; a concatenation boundary calculator that a concatenation boundary position in a region in which the recorded speech data and the rule-based synthetic speech data overlap, based on acoustic characteristics of the recorded speech data and the rule-based synthetic speech data that correspond to the text; a concatenative synthesizer that generates synthetic speech data corresponding to the text by concatenating the recorded speech data and the rule-based synthetic speech data that are segmented in the concatenation boundary position.