To perform the legato execution with natural feeling by uttering a musical sound with an utterance aspect not a legato utterance aspect when the performance with the legato execution isn't detected, and performing the musical sound with the selected legato utterance aspect when the performance with the legato execution is detected.

The note data answering to key operation are sent from a keyboard device 5 to a CPU 1, and when a value of a present note number CNN is '-1', that is, isn't the legato execution, the musical sound is generated with the regular utterance aspect. That is, the note number of the note data with this time of key depression is held to the present note number CNN, and the CPU 1 instructs a waveform reproducing device 6 to start waveform reproduction according to the value of a waveform number CWN, and sends out the value of the present number CNN, and sends out an envelope start instruction instructing the regular utterance aspect to an envelope generator 7. Further, when the value of the present note number CNN isn't '$1', that is, is the legato execution, the musical sound is generated with the legato utterance aspect according to a selected tone color.