PURPOSE: To considerably reduce the frequency in access to a main storage part to perform the interpolating operation.

CONSTITUTION: The data string of an electronic computer is received by a data input part 1 and is successively stored in a buffer memory 3. Meanwhile, an address input part 2 receives an input address and sends it as the internal address to an operation part 4. This part 4 generates a buffer address for data read required for interpolating operation based on the internal address and performs the interpolating operation based on data read out from the buffer memory 3, and the result is outputted to an output part 5.