PCR primers for detecting Bifidobacterium infantis comprising: a pair of a first oligonucleotide having a sequence of 20 or more continuous nucleotides selected from a nucleotide sequence of SEQ ID NO: 1 and a second oligonucleotide having a nucleotide sequence of SEQ ID NO: 2 or a nucleotide sequence of SEQ ID NO: 2 in which 0 to 7 nucleotides has been deleted from its 5'-terminal side is used to perform PCR using a chromosomal DNA or 16S rRNA of test bacteria as a template, and whether an amplicon of Bifidobacterium infantis is present or not is determined.