An input device for inputting a user instruction, comprising: an angular rate sensor configured to sense an angular rate at which the device rotates in the body frame to provide a first output; an acceleration sensor configured to sense an acceleration of the device in the body frame to provide a second output; a first operation unit configured to calculate a first rotation angle in the navigation frame based on the first output of the angular rate sensor; a second operation unit configured to calculate a second rotation angle in the navigation frame based on the second output of the acceleration sensor; an attitude angle measuring unit configured to calculate an attitude angle of the input device by combining the first rotation angle and the second rotation angle; an intensity calculation unit configured to calculate a force intensity in the navigation frame using the second output of the acceleration sensor and the attitude angle of the input device calculated by the attitude angle measuring unit; and an intensity mapping unit configured to perform mapping upon the calculated force intensity according to a predetermined mapping function, said predetermined mapping function having at least two of a depression area, a limitation area, and a scaling area, wherein (i) if the calculated force intensity falls within the depression area, the calculated force intensity is mapped to a depressed force intensity output according to the predetermined mapping function, (ii) if the calculated force intensity falls within the limitation area, the calculated force intensity is mapped to a limited force intensity output according to the predetermined mapping function, and (iii) if the calculated force intensity falls within the scaling area, the calculated force intensity is mapped to a proportionally scaled force intensity output according to the predetermined mapping function. an angular rate sensor configured to sense an angular rate at which the device rotates in the body frame to provide a first output; an acceleration sensor configured to sense an acceleration of the device in the body frame to provide a second output; a first operation unit configured to calculate a first rotation angle in the navigation frame based on the first output of the angular rate sensor; a second operation unit configured to calculate a second rotation angle in the navigation frame based on the second output of the acceleration sensor; an attitude angle measuring unit configured to calculate an attitude angle of the input device by combining the first rotation angle and the second rotation angle; an intensity calculation unit configured to calculate a force intensity in the navigation frame using the second output of the acceleration sensor and the attitude angle of the input device calculated by the attitude angle measuring unit; and an intensity mapping unit configured to perform mapping upon the calculated force intensity according to a predetermined mapping function, said predetermined mapping function having at least two of a depression area, a limitation area, and a scaling area, wherein (i) if the calculated force intensity falls within the depression area, the calculated force intensity is mapped to a depressed force intensity output according to the predetermined mapping function, (ii) if the calculated force intensity falls within the limitation area, the calculated force intensity is mapped to a limited force intensity output according to the predetermined mapping function, and (iii) if the calculated force intensity falls within the scaling area, the calculated force intensity is mapped to a proportionally scaled force intensity output according to the predetermined mapping function.