A software optimization device includes performance data storage unit to store data indicating performance of each system call, corresponding to a plurality of system calls, system call extraction unit to extract a system call described in a program source and similar-system-call detection unit to detect, from among the system calls the data indicating the performance of which is stored in the performance data storage unit, a system call having a function similar to that of the system call extracted by the system call extraction unit and having a performance better than that of the extracted system call.