In a sensor network system for transferring sensing data measured by a sensor node to a host server based upon a process condition, the process condition can be easily set. The host server (4) previously sets a transmission condition which is used to transmit only an event satisfying a preset condition to the host server (4). When the host server (4) receives a joined event from a PAN management server (2), the host server (4) transmits to the PAN management server (2) a transmission condition corresponding to an identifier of an ID of a sensor node (1) of a transmission source of the joined event, and the PAN management server (2) transfers only an observed event satisfying the transmission condition to the host server (4).