an electronic musical instrument having an automatic performance device includes a memory storing in addition to automatic performance data , envelope control data for controlling envelopes of automatic performance tones to be generated . the envelope control data has two logical values and is used for controlling the envelope of the tone at the decaying portion . the value &# 34 ; 0 &# 34 ; designates a gradual decay and the value &# 34 ; 1 &# 34 ; designates a quick decay . the automatic performance tones are respectively imparted with either of the gradual and the quick decay shapes suitable for the time intervals between the generated tones in the designated automatic performance pattern .