An automatic music transcription apparatus that can automatically transcribe a monophonic or polyphonic signal produced by a single musical instrument is provided. The apparatus includes an input block, an overtone-power-ratio detection block, a storage block, a chromatic-note-power detection block, an overtone elimination block for subtracting the product of the power of the fundamental note and the power ratio of each overtone corresponding to the chromatic note of the fundamental note from the power of the chromatic note of the overtone and adding the product of the power of the fundamental note, a musical-notation-information detection block, and a detection result output block for outputting the detected musical notation information to a file or the like.