PURPOSE: To facilitate input operation of data by displaying only the data that is possible for input at that point of time on a display plane corresponding to a input key.

CONSTITUTION: If a group of data to be inputted from adesignated switch 2 is assigned, its signal 20 is sent to a data reading circuit 5, and a group of data 22 assigned by the signal 20 is sent to a display device 3 and data selecting circuit 7 from a memory device 6. This display device 3 displays the data received from the data reading circuit 5 on a display plane of its corresponding key. Then, when an operator pushes a key, its corresponding signal 25 is sent to an input data selecting circuit 7, and data corresponding to the signal 25 are selected from the group of data that are previously held, and that data 26 are transferred to a keyboard part 9. Thus, the efficiency of inputting data is improved.