The conventional data transmitting/receiving system has problems: that a correct measurement cannot be performed because a measurement result is an addition of a verification processing time and a transmission time; that an authentication processing which is necessary for a transmission time measurement processing needs to be separately required; and that an unnecessary key exchange processing isexecuted. The transmission apparatus (a) shares authentication information with a request source which requests for transmission of content data, (b) transmits, to the request source, a measurement request generated using the authentication information, (c) receives, from the request source, a measurement response generated using the authentication information by the request source, as a responseto the measurement request, (d) measures the period of time from the transmission of the measurement request to the reception of the measurement response, as a round trip time, (e) transmits, to the request source, a measurement preparation request for a preparation which is necessary for generating the measurement response, before the transmission of the measurement request, and (f) determines that the request source is an eligible device as the transmission destination of the content data, after the measurement of the round trip time, in the case where it is confirmed that the round trip time is less than or equal to a reference value, the measurement response is verified as a correct response, and the measurement request is verified as a correct request by the request source.