PROBLEM TO BE SOLVED: To enhance security of a host system controlling a field device. SOLUTION: A control device 3 generates a first image which makes a selection of a control item of a field device 6 impossible and a second image which makes a selection of a control item of the field device 6 possible. Based on a display of the first image by an LCD 2, when a user possessing a radio mobile key 1 approaches the control device 3, the control device 3 receives a key signal D1 for permitting a selecting operation of the control item transmitted from the radio mobile key 1, and switches the first image displayed on the LCD 2 into the second image. Thus, by selecting and operating the control item of the field device 6 from the second image, a control of a setting change of the field device 6 can be permitted. As a result, security is enhanced by preventing a user who does not possess the radio mobile key 1 from operating the control device 3 and changing the setting of the field device 6. COPYRIGHT: (C)2011,JPO&INPIT
