It is one object of the present invention to provide effective optimization for a program that includes commands that may cause exception processes. A novel compiler for converting source code for a program written in a programming language into object code in a machine language comprises: an optimization execution unit for performing an optimization process for an object program written in a machine language; and a pre-processor and a post-processor for modifying the object program in order to absorb a difference in content between the point of origin of an exception process, which occurs in response to the execution of a command in the object program, and a location whereat the exception process is performed.