An electronic musical instrument uses a mouthpiece model that models a mouthpiece as a three-dimensional shape having one end at which the mouthpiece is to be held in a mouth of a performer being smaller than another end. A processor in the instrument calculates a reflection coefficient of a progressive wave and a regressive wave using the mouthpiece model by calculating a wave impedance for the progressive wave and calculating a wave impedance for the regressive wave, and generates a musical sound signal on the basis of the calculated reflection coefficient, which is then outputted to a sound generator for sound production.