An apparatus for multiplication, division and extraction of the square root which determines the value of a function of multiplication, division or extraction of the square root by iterated approximation includes a multiplier, adder/subtractor and shifter each having a predetermined bit width and connected to a bus. The output of the multiplier is inputted to the adder/subtractor or to the shifter and the result is again inputted to the multiplier through the bus. This operation is repeated. A shifter and a calculator connected to a second bus through a switch have a bit width greater than the predetermined bit width, are used for large-scale calculation and prevent a drop in calculation speed.