To simplify and accelerate data quotation by each recognizing a data registering destination through an operator does not remember it in a data processor with a data quoting function.

In the process of displaying character data such as a numerical figure, character and image data such as a graphic on a display part 2 in response to an input, the data processor optionally registers already displayed input data and executes the data quoting function for optionally quoting it as new input data. When data to be a registering object is designated-operated from among input data already displayed on the display part 2, the data quoting function prepares index data based on the data and displays this index data by fitting into the frames of keys N1 to N3 being indexes at the time of quoting registered data.