PURPOSE: To obtain triangular waves having different duty ratios and fixed amplitude, by converting an output of an up-down counter from digital to analog.

CONSTITUTION: The up-down counter is constituted as a 28 notation counter by two 24 notation counters 1, 2. Clock pulses P7, P6 having various kinds of frequency are applied to the counters 1, 2 through a data selector 3. A 28 notation programmable counter 4 is set up to apply the clock pulse P7 for counting-up to the counters 1, 2 and a 28 notation programmable counter 5 is set up to apply the clock pulse P8 for counting-down. A reference clock pulse PO is applied to the counters 4, 5 and the frequency dividing ratio is changed by a duty ratio setting switch 7. A counted value is converted into an analog signal by a D/A converter 9.