1. An information processing unit comprising: a memory part for storing in a file format therein information processing data containing Christian calendar year information having first number of digits; an application processing part for executing application processing by use of Christian calendar year information having second number of digits, of said Christian calendar year information having first number of digits contained in said data stored in said memory part; and a file access control part for writing/reading file format data to/from said memory part in response to a request from said application processing part; said file access control part including: a judgment part which upon a receipt of a request to read Christian calendar year information within a file stored in said memory part from said application processing unit, judges whether said Christian calendar year information in said memory part indicates a predetermined Christian calendar year onward; and a read Christian calendar year information output part which when it is judged in said judgment part that said Christian calendar year information indicates said predetermined Christian calendar year onward, generates Christian calendar year information having identification information indicative of that fact, to output it as read Christian calendar year information.