It is an object of the present invention to provide a method for suppressing non-specific reactions using a highly versatile method without affecting specific reactions. The present invention provides a detection method for detecting a target antigen in a sample using a specific antibody that specifically binds to the antigen, the method comprising: a) a step of bringing the sample into contact with a modified antibody; and b) a step of bringing the sample into contact with the specific antibody simultaneously with or after the step a), which is a highly versatile method that can suppress non-specific reactions.