To provide a method for testing a pathogen or a nucleic acid with a higher sensitivity than that of a nested PCR method.

This method for improving the detection sensitivity for the pathogen or nucleic acid is characterized by carrying out a PCR method, especially a two-stage PCR method such as the nested PCR method and then performing a Southern blot technique. The concentration of 10-8 pg/μl can be detected by combining the PCR method, especially the nested PCR method with the Southern blot technique and a remarkably high sensitivity as compared with single use of each technique can be obtained.