PURPOSE: To surely detect the presence or absence or quantity of Streptococcus mutans by bringing the monoclone antibody to the Streptococcus mutans or the polyclone antibody obtd. by immunizing this antigen with an animal into reaction with a sample to be inspected.

CONSTITUTION: The antigen specific to the Streptococcus mutans and the monoclone antibody to a serum type specific polysaccharide antigen or the polyclone antibody obtd. by immunizing this antigen with a mammal or birds are brought into reaction with the sample to be inspected and whether the antigen corresponding to the antibody exists in the sample to be inspected or not is decided by the presence or absence of an antigen-antibody reaction. Proper bacteria of either (a) type bacteria or (h) type bacteria are selectively used according to purposes for the serum type specific polysaccharide antigen of the Streptococcus mutans and the monoclone antibody and polyclone antibody for this antigen are obtainable according to the conventional practice.