A method of detection is provided that permits differentiation of each of Bacillus cereus, Bacillus thuringiensis, and Bacillus anthracis from other microorganisms, using oligonucleotide primers for amplification of the target nucleotide sequences characteristic to Bacillus cereus, Bacillus thuringiensis, and Bacillus anthracis, consisting of the oligonucleotide (A) having a nucleotide sequence obtained from SEQ ID NO:1 and containing at least one site that can amplify a nucleotide sequence characteristic to Bacillus cereus, the oligonucleotide (B) having a nucleotide sequence obtained from SEQ ID NO:3 and containing at least one site that can amplify a nucleotide sequence characteristic to Bacillus thuringiensis, and the oligonucleotide (C) having a nucleotide sequence obtained from SEQ ID NO:5 and containing at least one site that can amplify a nucleotide sequence characteristic to Bacillus anthracis. Also provided are a method of detection of Bacillus cereus, Bacillus thuringiensis, and Bacillus anthracis by polymerase chain reaction (PCR) using a primer specific to the DNA gyrase sub-unit B (gyrB) gene and a method of detection of Bacillus cereus, Bacillus thuringiensis, and Bacillus anthracis in a sample by differentiation on the genetic level.