A measuring system enabled to simultaneously start measurement by a plurality of transponders by communication between a reader/writer and a plurality of transponders each with a built-in sensor is to be provided. In addition to an identifier SID intrinsic to a sensor and a chip identifier TID intrinsic to a transponder chip, a unique identifier UID combining the sensor SID and the chip TID is provided in each transponder. A reader/writer, in designating a transponder and transmitting a measurement command to it, invalidates the chip TID out of the UID of each transponder, validates only information regarding a sensor function, and transmits measurement commands including action commands unique to each type of sensor.