Abstract: A sensor control circuit (25) periodically transmits a packet in synchronism with a change in a count value from a real-time clock circuit (22), which repeats a monotonous increment within a predetermined numerical value range, and also acquires and transmits the count value by adding the count value to the packet. A collection control circuit (14) acquires the value of a reference clock synchronized with the reference time of an upper network (NW) from a reference clock generation circuit (12) in accordance with reception of the packet, stores the value in a storage circuit (13) as a time stamp representing the arrival time of the packet, performs statistical processing of the time stamps and count values concerning a plurality of packets received, and corrects the time stamps concerning the packets based on an obtained packet transmission interval and a reference arrival time representing the arrival time of a head packet.

Abstract: Upon receiving a dummy packet, a data collection terminal slave device (2) appends, to a return packet, a timestamp indicating the reception time of the dummy packet and a timestamp indicating the transmission time of the return packet, and transmits the return packet to a data collection terminal master device (3). When performing a time synchronization process, the data collection terminal master device (3) transmits the dummy packet to the data collection terminal slave device (2).