A sensor net system including: a plurality of sensor nodes, where each sensor node is held on a person of a differing worker, and each sensor node includes; a sensor which obtains sensor data of a worker; a radio frequency circuit which notifies a server of the sensor data; and a server which includes: a unit for storing a relation list for correlating the sensor data with a work category of the worker; a unit for confirming location of the worker based on the obtained sensor data; and a unit for confirming a work category in which the worker is engaged based on the confirmed location and the relation list.