PURPOSE: To make the display easily visible by comparing it with a display executed with a reduced character by providing a specific controller.

CONSTITUTION: In an input data display system in the input field of the number of digits instructed in advance, a data input device is constituted of a controller 1, a display device 2, an input device 3 and storage devices 4-6, and the controller 1 is constituted of an input controller 10, a data form switching control part 11, an input data control part 12 and a data display control part 13. In such a state, the controller 1 executes the display by an enlarged character, and a reduced character, in the case enlarged character data does not exceed the designated number of digits, and in the case the data overflows from the designated number of digits and does not exceed double of the designated number of digits, respectively. In such a manner, in the case of the data in which utilization frequency of a larger number of digits than a prescribed number of digits is reduced, it is unnecessary to secure excessively input field length used usually, and usually, a display by a regular character can be enabled, therefore, it becomes easily visible, comparing with the reduced character. In this regard, at the time of switching the enlarged character and the reduced character, a special key is not required.