unknown signature is represented by other_n n is a nature number when the other_n is present in the comparison result it indicates that the failure signature has neither been defined nor been inputted into the failure signature database in step 227 if the hit ratio of the test result to at least one of the nth failure signature data is not equal to 0 then in step 231 the comparison result indicating that the test result is hit with the failure signature data is generated as mentioned above if the answer is no in step 221 step 229 is performed in step 229 if the last failure signature data is compared step 230 is performed if the last failure signature data is not compared step 232 is performed moreover in step 232 the present invention sets n n 1 and then comes back to step 221 to compare the n 1 th failure signature data in step 230 if the failure mode of the test result is not hit with all of the n failure signature data i e the failure mode of the test result is not included in any failure signature data then a comparison result indicating that the test result is an unknown signature is generated in step 228 otherwise a comparison result indicating that the test result is hit with the failure signature data is generated in step 231 after the comparison in step 22 is done and a comparison result.