A music piece analyzer includes: a key candidate determiner configured to analyze music data to determine a plurality of key candidates; and a key selector configured to extract each one of the plurality of key candidates, detect keys corresponding to related keys from among remaining ones of the plurality of key candidates supposing that the extracted one of the plurality of key candidates is a main key, on each extracted one of the plurality of key candidates, calculate a related key score in accordance with the number of the keys corresponding to the related keys, and select a key of a music piece in accordance with the related key score from among the plurality of key candidates.