PURPOSE: To perform the work without movement of a person by connecting one keyboard and plural CRTs at the time of using plural terminals by one person.

CONSTITUTION: A light emitting part 5 is provided with a small switch and light is turned on/off, and light is turned on only at the time of signal transmission, and a changeover switch 3 is provided with an LED, and the CRT connected at present is recognized. When a user will use a CRT 2A, he turns on the switch of the light emitting part 5 to irradiate a detecting part 1A with light. When the indicator LED of the changeover switch 3 indicates the CRT 2A, the CRT 2A can be operated on the keyboard. Thereafter, the switch of the light emitting part is turned off to prevent the other detecting part 1A from being irradiated with light. When he will use a CRT 2B, the detecting part 1B is irradiated with light by the same operation. When the light emitting part 5 is set to the user's head, he only turns to the CRT to be used to perform switching.