An observation unit of an authentication apparatus and an observation unit of an authentication target apparatus observe a radio wave from a common radio star at a common observation time. A sending unit sends information message including information on the observed radio wave, and an information reception unit receives it. An estimation unit estimates a position of the authentication target apparatus based on "the information on the radio wave observed by the observation unit" and "information on the radio wave observed by the observation unit". A retaining unit pre-retains positions of one or more authentication target apparatus(s). A determination unit checks whether a position of the authentication target apparatus pre-retained in the retaining unit and the estimated position correspond within a predetermined error range, and settles authentication for the information message as a success in a case where the positions correspond.