PURPOSE: To furnish a device which can display accurately for practical use delicate sounds such as musical sounds based on a just tone scale in relation to an average tune scale employed widely in a musical performance.

CONSTITUTION: An arithmetic circuit (Kyn arithmetic circuit), which receives as an input an output signal of a period counter counting the number (t) of pulses obtained by controlling a clock pulse output of a reference pulse generator with an analog input signal of a musical sound and operates [12log (16F/An.t)/log2] +1, where F is the frequency (Hz) of said clock pulse and An a standard pitch (Hz), is provided. A Kyn value, which is an output of said Kyn arithmetic circuit, is supplied from a first output terminal shown in the figure to the outside. According to an embodiment shown in the figure, a rounding arithmetic circuit (KynRnd arithmetic circuit) is provided, and thereby a numerica value (KynRnd value) obtained by rounding a numerical value of about 10 cents of an output of the Kyn arithmetic circuit can be supplied from a second output terminal. The Kyn value delivered from the first output terminal, which is an output of the Kyn arithmetic circuit, is constantly in accord with the key number of a piano on the market corresponding to the frequency value of an input signal. Namely, an output value of said output terminal is a value obtained by converting the input signal of the device into the key number of the piano on the market. According to the embodiment of the device of this invention wherein the arithmetic circuit is incorporated, an outside signal input having highly multiform frequencies is converted and arranged into a signal output of the closest sound on a staff noted according to an average tune scale, and is output for display.