An inclination calculation apparatus within a game machine computes an inclination of an input device having an acceleration sensor/detector capable of simultaneously detecting an acceleration in at least two axial directions. Programmed logic circuitry within the apparatus consecutively generates preliminary data which represents an inclination and which is uniquely determined from acceleration data consecutively output from the acceleration sensor/detector. Programmed logic circuitry within the apparatus also consecutively computes a new/updated inclination based on a previously computed inclination, an acceleration due to gravity and a current inclination represented by the preliminary data, wherein the new/updated inclination is computed to have a direction oriented between the previously computed inclination and a current inclination represented by the preliminary data by a degree to which the acceleration due to gravity contributes to the acceleration data.