1. An arithmetic operation system for arithmetically operating a first operand having an actual point and a second operand having no actual point; said system comprising: (a) an actual point detector for detecting a position of said actual point of said first operand to output a first position data and a bit number data; (b) a first register for storing said first position data; (c) a second register for storing said bit number data; (d) a shifter for shifting left said first operand by specific bits according to said bit number data stored in said second register to output a third operand having no actual point; (e) an integer arithmetic operator for arithmetically operating said second and third operands to output a first operation result; (f) an assumed point designator for designating a position of an assumed point of said first operation result according to said first position data; and (g) a rounder for rounding said first operation result according to said designated assumed point of said first operation result by said assumed point designator to output a second operation result; wherein said shifter is also for shifting right said second operation result by said specific bits according to said bit number data to output a third operation result having no actual point, and wherein said third operation result represents a rounded operation result of said first and second operands.