An electronic musical instrument capable of producing an attack repeat effect. The attack repeat effect is a musical effect produced by repeated occurrences of attack and decay during a single continued sounding of a musical tone, giving to an audience an impression as if the tone started and stopped repeatedly. According to the invention, a complete envelope shape starting by an attack portion and ending by a decay portion is stored in a memory. When a key on the keyboard is depressed, the stored envelope shape is read from the memory and, upon completion of reading of one cycle of the envelope shape, reading of the envelope shape is resumed from the beginning. A time division multiplexed reading out of the envelope shape is conducted with respect to a plurality of channels. The read out envelope shape is used for controlling the amplitude of the musical tone signal. If the key is released, reading of the envelope shape is no longer repeated for a next and subsequent cycles.