A harmony adaptor is optionally usable as an attachment to a karaoke apparatus which has a pickup device for collecting a live singing sound and converting the same into a vocal signal, and a mixing device for mixing the vocal signal with a music signal representative of a karaoke music sound and for acoustically reproducing the live singing sound accompanied by the karaoke music sound according to the mixed ones of the vocal signal and the music signal. The harmony adaptor is detachably connectable to the pick-up device for receiving therefrom the vocal signal. The harmony adaptor generates a harmony signal which originates and separates from the received vocal signal and which represents a harmony chorus sound made consonant with the live singing sound. The harmony adaptor is detachably connectable to the mixing device for transmitting thereto the received vocal signal and the generated harmony signal concurrently with each other so as to enable the mixing device to acoustically reproduce the harmony chorus sound according to the transmitted harmony signal along with the live singing sound and the karaoke music sound.