Abstract: An inner product calculating circuit is provided to calculate an inner product of a constant vector and an input vector, where both of the vectors consist of m respective elements (m being an integer, m>2), the elements of the constant vector can be expressed as the sum and difference of I weighted coefficients (I being an integer, I<m), and the weights applied to the I coefficients are selected from the group consisting of 0 and powers of 2. This inner product calculating circuit is comprised of adder-subtracter circuits for adding respective elements of the input vector with weights of the coefficients extracted from all elements of the constant vector, and multiplying circuits for multiplying outputs of the adder-subtracters with the respective coefficients.