Patent ID: 8457548

Claim:
A relay device which is connected to an external device periodically transmitting and receiving data including numerical information and identification information of the numerical information, and relays transmission and reception of data between external devices, comprising: a first communication section for performing transmission and reception of data with the external device; a data storage section for storing data; a second communication section for communicating with another relay device; a first buffer for storing, each time data is received from the external device, numerical information of the received one or more data; and a controller for reading out the numerical information stored in said first buffer and creating a data frame including the numerical information for a certain period of time, wherein the second communication section transmits the created data frame to another relay device, the relay device further comprises a second buffer for storing, when a data frame is received from another relay device, the received data frame or the numerical information included in the data frame, said controller updates the numerical information of data stored in the data storage section with the numerical information stored in said first and second buffers, said controller judges whether or not a notice of determination indicating determination of data to be stored in the data storage section is received from another relay device, and said controller updates the numerical information when it is judged that the notice of determination is received.