Apparatus for calculating a plurality of interpolation values is adapted to calculate linear interpolation values, consisting of a second data train, from a first data train and includes a memory for storing the first data train and a calculator for calculating the interpolation value from the corresponding two data in the first data train read out of the memory. The calculator comprises an n-bit register for designating those addresses of the memory where data to be read out of the upper m-bit section of the n-bit register is stored and for determining weighted factor data for calculating the interpolation value at the lower (n-m) bit section of the register, a calculating unit for calculating the interpolation value from the data read out of the memory and the weighting coefficient data, an adder for adding a position increment value for designating the adjacent interpolation value to the register each time each interpolation value is calculated at the calculating unit, and a counter stepped one count for each calculation of each interpolation value and adapted to send an end signal to a central processing unit when a predetermined number of counts are completed. The memory, register, adder and counter are controlled by the central processing unit.