To provide an assistant base for a sequencer which makes it possible the arrange the sequencer at an easy-to-operate position for an upright piano.

The assistant base 10 for the sequencer 1 consists of two engagement plates 11 and 12 and two bridging plates 13 and 14. The engagement plates 11 and 12 have engagement parts 11a and 12a for engaging the upper end part with the upper edge of the top front plate 5 of the piano and also has abutting parts 11b and 12b made to abut against the upper front plate 5 vertically and holding parts 11c and 12c for holding the sequencer 1. The bridging plates 13 and 14 have holes which are wide enough to insert screws 15. The bridging plates 13 and 14 are arranged laterally bridging the engagement plates 11 and 12 and assembled with the screws 15. Consequently, the assistant base 10 is installed in front of the upper front plate 5 of the piano and the sequencer 1 is mounted on it, so a player on a chair can easily operate the sequencer 1.