The invention discloses an automatic performance apparatus and a computer implementation method for executing automatic performance by using a plurality of audio waveform data stored in a storage section. A plurality of sets of waveform data and switchover position information indicative of, for each of the sets of waveform data, one or more possible switchover positions in the waveform data are pre-stored in memory, and one set of waveform data is reproduced in accordance with the passage of time. During reproduction of a first set of waveform data, a second set of waveform data is designated at given timing in response to a user's instruction. Control is performed such that the waveform data to be reproduced is switched from the first set of waveform data over to the second set of waveform data in response to waveform data reproduction timing arriving at one of the possible switchover positions indicated by the switchover position information corresponding to the second set of waveform data. Reproduction of the second set of waveform data is started at the switchover position corresponding to the reproduction timing.