A controller interface processor of a user interface apparatus acquires the tilt of a game controller as a rotational value from a sensor built in the game controller. An operation amount determining unit selects a sensitivity characteristic pattern from a plurality of sensitivity characteristic patterns different in the reaction sensitivity of an operation amount with respect to the rotational value in accordance with the width of a range of the rotational value, refers to the selected sensitivity characteristic pattern, and determines the operation amount corresponding to the rotational value acquired.