PURPOSE: To reduce operation misses by informing transmission or the kind of transmitted data to the operator in a data terminal device of a telephone data entry system.

CONSTITUTION: The data to be entered is inputted from an operation part 8 of the data terminal device 1 to a control part 9 by keying. The input data are displayed on a display part 12 so that the operator can check the data, and simultaneously registered in a storage part 10. After completing registration of the data group, the storage part 10 is coupled with a center device through an interface 11 and the data are successively transmitted to the center device. Since the display part 12 displaying data in accordance with the information outputted from the control part 9 is connected, the operation misses can be prevented.