A communication processing apparatus alternately transmits a carrier wave carrying a command and receives a response from a tag while transmitting an unmodulated carrier wave. A transmission control unit changes the phase of the unmodulated carrier wave transmitted from a transmission/reception circuit in response to start of reception of the reflected wave from the tag. The transmission/reception circuit includes a circuit for separating and detecting an I signal and a Q signal included in the reflected wave from the tag. A phase detection unit uses the I signal and the Q signal to detect change of the phase of the reflected wave. A distance calculation unit measures a time from a change of the phase of the unmodulated carrier wave to a detection of a corresponding change in the phase of the reflected wave, and uses the time to calculate the distance from the antenna to the tag.