PROBLEM TO BE SOLVED: To provide a system capable of recognizing whether there is an instruction from an instructor with an extremely small time lag, for the image of an object.SOLUTION: An object image transfer means 4 of an instructed device 2 receives an object image such as an echo image, and executes control to transmit it from an instructed device communication unit 6. At the time, the object image which is a transmission object is not displayed on an instructed device display unit 8. The object image display means 26 of an instruction device 20 executes control to display the object image, received by an instruction device communication unit 22, on an instruction device display unit 24. A confirmed object image transmission means 28 sends back the object image, to which instruction contents have been added by an instructor, as a confirmed object image by the instruction device communication unit 22. The confirmed object image display means 10 of the instructed device 2 which has received the confirmed object image displays it on the instructed device display unit 8.
