An estrus notifying apparatus (104) receives from a relay device (102), measurement result information of a step count transmitted by a communications device (101) attached to a livestock animal (A). The estrus notifying apparatus (104) determines based on the measurement result information, whether the livestock animal (A) is in an abnormal state. The estrus notifying apparatus (104), upon determining an abnormal state and receiving from a worker (W), notification that the livestock animal (A) will be attended to, sets the communications device (101) of the livestock animal (A) to be a tracking target. The estrus notifying apparatus (104), via a relay device (102), transmits to the communications device (101), a change instruction to set the transmission interval for the measurement result information to be short. The communications device (101) shortens the transmission interval based on the received change instruction. Thereafter, the estrus notifying apparatus (104) notifies a worker (W) of position information correlated with the new relay device (102), each time the relay device (102) used to report measurement result information by the communications device (101) set to be a tracking target changes.
