PURPOSE: To perform an inventory processing at any time by performing updating to a value for which the value of a difference stored in an adjustment quantity storage part is added to the quantity data of a quantity storage part.

CONSTITUTION: When the quantity data outputted to an output device 4 is not a correct value, the correct value is inputted from an input device 1 and is stored in an inventory real number storage part 23. An adjustment quantity calculation part 33 calculates the difference between a quantity stored in the inventory real number storage part 23 and the quantity stored in a book balance storage part 22 and sends the result to the adjustment quantity calculation part 33 to be stored. A quantity updating part 34 adds the quantity data stored in a quantity storage part 21 and the quantity stored in the adjustment quantity calculation part 33 at the optional point of time, sends the result to the quantity storage part 21 to be updated and outputs the result to the output device 4. Thus, the quantity data stored in the quantity storage part 21 are corrected to the corrected value by the inventory processing.