A mathematical calculator where when a mixed fraction key is depressed, an integer part input area, a numerator input area, a denominator input area and a vinculum for a mixed fraction are displayed on a display screen. When a user depresses a “1” key of a numeric keypad, “1” is inputted and displayed to and on the integer part input area. When the user depresses a “+” operator key, a CPU prohibits the inputted “+” operator from being inputted and displayed to and on the integer part display area. When the user depresses the “+” operator key in a state in which “(1” is inputted and displayed to and on the integer part input area, the CPU allows the inputted “+” operator from being inputted and displayed to and on the integer part display area.