PURPOSE: To prevent erroneous setting of the input mode by providing plural input means which are depressed in the operation period of an input pen to change the input function of the input pen to a prescribed function only in the operation period.

CONSTITUTION: An operator inputs information to a digitizer 1 with an input pen 3 in his right hand while depressing one of shift keys 4L, which are displayed on a function display part 5 and correspond to desired functions, which his left hand. Thus, its input function is used to input information.