PURPOSE: To obtain an oscillating output of high accuracy, by calculating and storing a product obtained by multiplying a digital signal sampled with a prescribed sampling frequency by the 1st digital coefficient, the 2nd digital coefficient and the calculated result obtained earlier by a sampling period respectively.

CONSTITUTION: A digital signal V(nT) sampled with a prescribed sampling frequency FS is supplied to an input terminal 1 and multiplied by the 1st digital coefficient C1 through a multiplier 2. A data selector 3 selects data with a selection pulse t1, and the code is checked by a decoder 6. Then the addition or subtraction is selected by an FF7. An adder 4 performs an addition with a sampling period earlier output y(nT) supplied from a D-FF5, and then C2 is selected and added. In this case, if the adder 4 has an overflow, this overflow is detected by the decoder 6. The output of addition is inverted to deliver the correct value in the form of a triangular wave. At the same time, a subtraction is carried out via the FF7. These actions are repeated to obtain an oscillating output of a triangular wave. Both oscillating frequency and control sensitivity can be controlled by changing the coefficients C1 and C2.