A communications device (101) transmits measurement result information (110) indicative of the step count of a livestock animal (A) to a relay device (102) located in a communications area (103). The relay device (102) receives the measurement result information (110) from the communications device (101) and transmits the measurement result information (110) to an estrus notifying apparatus (104). The estrus notifying apparatus (104) stores the communications devices (101) equipped to respective livestock animals making up a herd and GPS communications device (107) equipped to any of the livestock animals making up the herd in a correlated manner for each herd. If it is determined that the measurement result information (110) received from the relay device (102) satisfies a given condition, the estrus notifying apparatus (104) searches for the GPS communications device (107) correlated with the communications device (101). The estrus notifying apparatus (104) transmits activation instruction information (130) to the GPS communications device (107). The GPS communications device (107) receives the activation instruction information (130) and turns on a power source.
