PURPOSE: To obtain an output digital signal to multiply a desired coefficient to an input digital signal and to delete the total number of gates by selectively switching a multiplication coefficient set by respective switching means by input data.

CONSTITUTION: Input digital signals I1WIm are inputted to a first switching means 100, and the output made A1-fold or B1-fold by a first bit D1 of input data is sent to a next step. A second switching means 101 sends the output made A2-fold or B2-fold by a second bit D2 to a next step and a third switching means 102 sends the output made A3-fold or B3-fold by a third bit D3. Consequently, when the selected coefficient is for example, A1, B2 and A3, A1.A2.A3- fold made output digital signals O1WOm can be obtained. When the coefficient of the switching means is expressed by a general formula, it is expressed by a formula I provided that Xn=the inverse of 2n-1, n=1Wn. Thus, realization can be performed by a small number of gates and since the connection, which becomes a light load, can be executed, and action speed can be hastened.