To provide a protection system of personal information of a user (dealer) in a terminal device of a telephone conversation system.

The terminal device 2 is used for the communication system which comprises a visible displaying part 24 which displays various operation keys such as dial keys 25, circuit keys 22, etc., data, and other items. The device comprises a measure to erase display of the visible displaying part when the terminal device 2 is in a condition of not being used, and it is detected that various operation keys are not operated for a constant time, and a measure to return the display, when it is recognized that an operation is conducted by a specified operator, when there are operation for the device made afterwards.