To realize the cost reduction of laying work by eliminating cables for connecting discretely set various sensors to a monitor device body.

The process value of a plant detected by an intelligent sensor (sensor) 15 having a communicating means is transmitted through a speech communication network 24 to a data collecting and displaying device by PHS communication so as to be monitored. Also, a diagnostic device 20 requests the transmission of the self-diagnostic result of the sensor 15, and obtains and diagnoses the result. Also, an engineering device 21 sets and changes various set values, and transmits the set value to the sensor 15 so that the set value can be set and changed. Also, a portable information collecting and displaying device 22 obtains the detected value from the sensor 15, and confirms the detected value at a job site near the sensor 15. Also, a portable engineering device 23 sets and changes the set value of the sensor 15 near the sensor. Thus, the transfer of the various information can be performed by using the PHS communication.