There is provided an interrogator, transponder, and transponder identification method, which shorten processing time for identification. An interrogator that makes wireless communication with a transponder, comprising: a temporary number specify section that transmits a request for transmission of a unit bit string as a bit string having a predetermined length in a bit string expressing a temporary number owned by the transponder, receives a unit bit sting transmitted from the transponder in response to the request, and specifies the temporary number of the transponder, based on the unit bit string; and an identification information obtaining section that transmits, if a temporary number of a transponder is specified by the temporary number specify section, a request for transmission of identification information of the transponder to the transponder, and receives the identification information transmitted from the transponder, in response to the request.