PURPOSE: To use a control circuit in many action modes and to attain a compact and light-weight constitution of a data terminal device, by using an action mode register to switch the control logics of the writing and reading control circuits.

CONSTITUTION: In a data input mode an action mode register 24 is set at a data input mode by a key input circuit 25. Thus a mode designating signal A to designate the data input mode in delivered from the register 24. Then a writing control circuit 20 can be actuated and the data given from a key input circuit 25 is transferred to a main memory part 9. When the register 24 is set at a retrieval correction mode, a reading control circuit 21 reads out the data stored in the part 9 and transfers it to a display circuit 22. In a correction mode the correction data is supplied from the circuit 25 by referring to the display data. Then the circuit 20 operates to give a correction display. At the same time, the correction data is also transferred to the part 9.