To extract interference part of a global variable, having the possibility of occurrence of problems caused by the interruption during the time starting from read processing to write processing of the global variable, and to automatically check the existence of interrupt disable/enable instructions on proper positions.

The read processing and the write processing satisfying predetermined conditions are determined in every processing description of the global variable, on the basis of a source program, and a variable attribute table is generated. When the write processing of the global variable is performed in the upper function (S120), and a pair of read processing and write processing satisfying the conditions are performed in a lower function (S130), on the basis of the variable attribute table, the existence of interrupt disable/enable instructions on proper positions corresponding to the pair description position in the lower function, is determined (S140-S160), and a result of the determination is outputted (S170).