1. A data input device that includes two input units including a character string input unit that accepts a character string and a voice input unit that accepts voice input, a display unit that displays a character string, and a speech recognition dictionary, the data input device comprising: a dynamic speech recognition dictionary generator that extracts phrases of which heads match a head of a character string inputted through the character string input unit from phrases stored in the speech recognition dictionary, and generates a dynamic speech recognition dictionary that stores difference phrases, the difference phrases each being part of an extracted phrase excluding a common phrase that is common among the extracted phrases; a display controller that displays the difference phrases of an input character string candidate being highlighted on the display unit; a speech recognizer that carries out speech recognition of voice inputted through the voice input unit by using the dynamic speech recognition dictionary; and an input character string confirmer that confirms the input character string candidate that includes a difference phrase recognized by the speech recognizer as an input character string, wherein at least one of the dynamic speech recognition dictionary generator, the display controller, the speech recognizer and the input character string confirmer is included in a processor.