A computer readable storage medium having stored thereon a game program to be executed by a computer of a game apparatus, the game program causing the computer to act as: operation data obtaining means for obtaining operation data including at least acceleration data and angular velocity data from an input device including at least an acceleration sensor and a gyrosensor; posture calculation means for calculating a posture of the input device based on the acceleration data and the angular velocity data, first calculation means for calculating a center of a rotation motion applied on the input device and a radius of the rotation, based on the acceleration data and the angular velocity data; second calculation means for calculating a velocity vector indicating moving velocity of the input device in the rotation motion, based on the radius of the rotation, and game processing means (S7, S8) for executing game processing based on the calculated velocity vector and/or the radius of the rotation wherein the game processing means determines a posture, in a virtual game space, of an operation target object, which is a target of an operation made by a player, based on the posture of the input device, and determines a position of the operation target object based on the velocity vector, the game processing further sets a first parameter in accordance with a first axis component of the three axis components composing the velocity vector, sets a second parameter in accordance with lengths of predetermined two axis components including the first component, and updates, based on the first parameter and the second parameter, the position and the posture of the operation target object. operation data obtaining means for obtaining operation data including at least acceleration data and angular velocity data from an input device including at least an acceleration sensor and a gyrosensor; posture calculation means for calculating a posture of the input device based on the acceleration data and the angular velocity data, first calculation means for calculating a center of a rotation motion applied on the input device and a radius of the rotation, based on the acceleration data and the angular velocity data; second calculation means for calculating a velocity vector indicating moving velocity of the input device in the rotation motion, based on the radius of the rotation, and game processing means (S7, S8) for executing game processing based on the calculated velocity vector and/or the radius of the rotation wherein the game processing means determines a posture, in a virtual game space, of an operation target object, which is a target of an operation made by a player, based on the posture of the input device, and determines a position of the operation target object based on the velocity vector, the game processing further sets a first parameter in accordance with a first axis component of the three axis components composing the velocity vector, sets a second parameter in accordance with lengths of predetermined two axis components including the first component, and updates, based on the first parameter and the second parameter, the position and the posture of the operation target object.