Provided is a sensor network system including sensor master devices (15A to 15D) which receive detection information obtained by sensors (11A to 11F) through wireless communication, a data server (17) which acquires the detection information from the sensor master devices (15A to 15D) through power line communication, and notification devices (13A, 13B) which receive notification information from the data server (17) to perform notification, in which the sensor master devices (15A to 15D) are connected to the sensors (11A to 11F) and the notification devices (13A, 13B), and the data server (17) determines an object to be notified in accordance with, for example, a detection position which is detection information for at least one of an object to be notified and notification contents, on the basis of the acquired detection information.