The flag access failure checking apparatus detects flags (S 01, S 02) from among computer programs that execute two or more different processes using flags that can set only two values and execute the statements to access the flag (D 05), processing contents for the flag in the statement (D 06), and statement execution order (D 08) (S 04, S 05, S 07). Based on the processing contents (D 06) for the flag and the order of execution (D 08) of the statement, it is judged whether there is a possibility that it can not be executed by switching two or more different processing using flags (S 08 to S 11) (S 12).
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