A sound effect imparting apparatus, which is employed in the electronic musical instrument in order to impart a variety of sound effects to the musical tones in a variety of manners, is mainly configured by an effect program memory, a sound-effect operation portion, a mixer and a mixing information supply portion. The effect program memory stores a plurality of effect programs, respectively corresponding to a plurality of sound effects to be imparted to musical tone data, in advance. The sound-effect operation portion performs arithmetic operations and/or logical operations on its input data in accordance with the effect programs read from the effect program memory, thus imparting desired sound effects to the musical tone data. The mixer receives the musical tone data, given from an external device, and operation data, outputted from the sound-effect operation portion, representing the musical tone data to which the sound effects have been imparted. Thus, the mixer selects some of the data inputted thereto in accordance with mixing information given from the mixing information supply portion, so that the selected data are mixed together; and consequently, mixed data are supplied to the sound-effect operation portion. On the basis of the mixed data outputted from the mixer, the musical tones to which several kinds of sound effects are imparted can be produced.