To provide a device and a method for easily and quickly detecting and analyzing gram-positive bacteria in a specimen and to provide a device and a method for easily, quickly and accurately detecting and analyzing gram-negative bacterial and gram-positive bacteria in a specimen.

In the preparation of a test substance from a specimen, the specimen is treated in a manner to generate an optical information difference between the gram-negative bacteria and the gram-positive bacteria in the specimen. Optical information is detected from individual particle in the test substance and the gram-positive bacteria in the specimen is analyzed based on the detected optical information.