PURPOSE: To increase the frequency receiving a strong electric field by providing two antennas to a transponder radio equipment and switching the antennas.

CONSTITUTION: Antennas 6a, 6b are switched at a time interval such as a time interval a little longer than an abnormality alarming data length of a transponder radio equipment terminal 1 after the end of confirming test automatically. Thus, the alarming data from the transponder radio equipment 1 is received by an antenna with a stronger electric field in the antennas 6a, 6b. Then the received signal is given to a central management center from a controller 2 through a wired line and the abnormality is informed. Thus, the frequency of receiving a strong electric field of the transponder radio equipment is increased even with the fluctuation of the electric field.