Distance measuring equipment comprising: a transponder configured to transmit a reply in response to an interrogation input thereto, the interrogation comprising twin pulses composed of a pair of pulses having a prescribed spacing; and a monitoring processor configured to transmit to the transponder a pseudo interrogation identical in format to the interrogation, receive from the transponder a reply responding to the pseudo interrogation, and monitor a performance of the transponder, the monitoring processor comprising: a pulse spacing adjuster configured to adjust a pulse spacing of a pair of pulses constituting twin pulses of the pseudo interrogation along with generation of the pseudo interrogation; and a monitor configured to output an alarm in response to a failed reception of, or a delayed reception of, or a decreased response efficiency of, a reply from the transponder after transmission of the pseudo interrogation, or an increased or decreased transmission rate thereof; the monitor comprising a pulse pair detector configured to detect from among signals input thereto from the transponder a pulse pair in a reply, as twin pulses having a compliant pulse spacing; a delay monitor configured for comparison between the timing of the transmission of the pseudo interrogation and the timing of input of a corresponding reply, to check for a delay of the reply, to output the alarm; a response efficiency monitor configured for determination of a response efficiency of the transponder depending on the number of the replies input and the number of pseudo interrogations transmitted, to check for a decreased response efficiency, to output the alarm; and a transmission rate monitor configured to check for an increased or decreased transmission rate, to output the alarm. a transponder configured to transmit a reply in response to an interrogation input thereto, the interrogation comprising twin pulses composed of a pair of pulses having a prescribed spacing; and a monitoring processor configured to transmit to the transponder a pseudo interrogation identical in format to the interrogation, receive from the transponder a reply responding to the pseudo interrogation, and monitor a performance of the transponder, the monitoring processor comprising: a pulse spacing adjuster configured to adjust a pulse spacing of a pair of pulses constituting twin pulses of the pseudo interrogation along with generation of the pseudo interrogation; and a monitor configured to output an alarm in response to a failed reception of, or a delayed reception of, or a decreased response efficiency of, a reply from the transponder after transmission of the pseudo interrogation, or an increased or decreased transmission rate thereof; the monitor comprising a pulse pair detector configured to detect from among signals input thereto from the transponder a pulse pair in a reply, as twin pulses having a compliant pulse spacing; a delay monitor configured for comparison between the timing of the transmission of the pseudo interrogation and the timing of input of a corresponding reply, to check for a delay of the reply, to output the alarm; a response efficiency monitor configured for determination of a response efficiency of the transponder depending on the number of the replies input and the number of pseudo interrogations transmitted, to check for a decreased response efficiency, to output the alarm; and a transmission rate monitor configured to check for an increased or decreased transmission rate, to output the alarm. a pulse spacing adjuster configured to adjust a pulse spacing of a pair of pulses constituting twin pulses of the pseudo interrogation along with generation of the pseudo interrogation; and a monitor configured to output an alarm in response to a failed reception of, or a delayed reception of, or a decreased response efficiency of, a reply from the transponder after transmission of the pseudo interrogation, or an increased or decreased transmission rate thereof; the monitor comprising a pulse pair detector configured to detect from among signals input thereto from the transponder a pulse pair in a reply, as twin pulses having a compliant pulse spacing; a delay monitor configured for comparison between the timing of the transmission of the pseudo interrogation and the timing of input of a corresponding reply, to check for a delay of the reply, to output the alarm; a response efficiency monitor configured for determination of a response efficiency of the transponder depending on the number of the replies input and the number of pseudo interrogations transmitted, to check for a decreased response efficiency, to output the alarm; and a transmission rate monitor configured to check for an increased or decreased transmission rate, to output the alarm.