A computer-readable storage medium having stored thereon a game program executable by a computer of a game apparatus for executing game processing in accordance with a movement of an input device, wherein the game program causes the computer to execute: an obtaining step of obtaining an acceleration generated in at least two predetermined axial directions of the input device repeatedly; a change amount calculation step of calculating a change amount of each of the accelerations obtained in the obtaining step during a predetermined time period; an accumulated value calculation step of calculating an accumulated value obtained by accumulating the calculated change amounts; a swing strength calculation step of calculating a swing strength of the input device based on the accumulated value; and a game processing step of executing the game processing using the calculated swing strength, wherein: the input device comprises an acceleration sensor for detecting an acceleration in at least two predetermined axial directions; and in the obtaining step, the computer calculates, as an acceleration to be obtained, a vector which changes so as to follow a vector represented by data output from the acceleration sensor and in the obtaining step, the computer calculates, as an acceleration to be newly obtained, a vector internally dividing a range between a vector representing the current acceleration and a vector represented by data output from the acceleration sensor. an obtaining step of obtaining an acceleration generated in at least two predetermined axial directions of the input device repeatedly; a change amount calculation step of calculating a change amount of each of the accelerations obtained in the obtaining step during a predetermined time period; an accumulated value calculation step of calculating an accumulated value obtained by accumulating the calculated change amounts; a swing strength calculation step of calculating a swing strength of the input device based on the accumulated value; and a game processing step of executing the game processing using the calculated swing strength, wherein: the input device comprises an acceleration sensor for detecting an acceleration in at least two predetermined axial directions; and in the obtaining step, the computer calculates, as an acceleration to be obtained, a vector which changes so as to follow a vector represented by data output from the acceleration sensor and in the obtaining step, the computer calculates, as an acceleration to be newly obtained, a vector internally dividing a range between a vector representing the current acceleration and a vector represented by data output from the acceleration sensor. the input device comprises an acceleration sensor for detecting an acceleration in at least two predetermined axial directions; and in the obtaining step, the computer calculates, as an acceleration to be obtained, a vector which changes so as to follow a vector represented by data output from the acceleration sensor and in the obtaining step, the computer calculates, as an acceleration to be newly obtained, a vector internally dividing a range between a vector representing the current acceleration and a vector represented by data output from the acceleration sensor.