PURPOSE: To let a beginner understand musical scale constitution through simple operation by placing a flat plate on a disk on which alphabets for scale display, tetrachords, and a keyboard with scale clef are marked at the circumference, and allowing the disk to rotate freely and thus displaying the constitution of musical scales.

CONSTITUTION: A disk is marked with alphabets for scale display at intervals of 5° on the circumference, with tetrachords of respective musical scales in circular staff notation coaxially with said circle of alphabets, and keyboard with scale clef is displayed on the disk coaxially also with the circle of tetrachord. A flat plate 2, on one hand, has a proper opening to see a corresponding part of the scale clef, two successive tetrachords, and a corresponding part of the keyboard through the opening. While the flat plate 2 is positioned on the top surface, the disk is rotated freely.