PURPOSE: To reduce the capacity of an interlock table and increase the processing speed, by processing data while checking if for validity in byte units with the interlock table.

CONSTITUTION: Data 31W33 before conversion consisting of plural discontinuous bytes are divided into byte units of the number of hundreds, the number of tens, and the number of units and are checked for validity in order from the most significant byte with interlock tables 34W36. That is, data is judged as valid when it is not registered as invalid and conditions of invalidness are not satisfied. Next, the absolute address of a conversion table 37 is detected. Contents of the interlock table 34, the number of tens, and the number of unit are added to detect the absolute address of the conversion table 37.