OPTIMIZATION OF CONVERSION OF A CHARACTER CODING SYSTEM

A compiler optimizing conversion of a character coding system for a character stored in a string variable in a target program to be optimized has a conversion instruction generation section which generates a conversion instruction to convert a character from a first character coding system to a second character coding system and to store the converted character in the string variable, the conversion instruction being generated before each of a plurality of procedures by which the character in the string variable written in the first character coding system is read out and is used in the second character coding system, and a conversion instruction removal section which removes each of conversion instructions generated by the conversion instruction generation section if a character in the second character coding system is stored in the string variable in each of the execution paths executed before the conversion instruction.