An electrical musical instrument includes a scale designator for sequentially and automatically designating a scale on the basis of prestored data of a music piece, and a musical tone signal generator for outputting a musical tone signal including a harmonic frequency on the basis of the scale designated by said scale designator or as a fundamental frequency. A voice detector detects an external voice and the detected voice is divided by a modulator into voice signals in a plurality of frequency ranges. The musical tone signal is modulated in units of corresponding frequency ranges on the basis of the voice signals divided into the plurality of frequency ranges.