A digital signal processor for computing a vector product between a column vector input signal including a plurality of data items (x0, x1, x2, . . . , x7) and a matrix including a predetermined number of coefficient data items so as to produce a column vector output signal including a plurality of data items (y0, y1, y2, . . . , y7). In a first cycle, the leading data x0 of the column vector input signal is stored in a first store unit (Rin), whereas during this period of time, in a second cycle shorter in time than the first cycle, the data items (c0, c1, c2, . . . , c7) in the row direction constituting a first portion of the matrix are sequentially read out such that both data items are multiplied, thereby storing the multiplication results in an accumulator. A similar data processing is repeatedly executed so as to obtain, based on the outputs from the accumulator, a column vector output signal constituted by the plurality of data items (y0, y1, y2, . . . , y7).