A motion determining apparatus for determining a motion of an input device including an acceleration sensor for detecting an acceleration in each of at least two axial directions, the motion determining apparatus comprising: data obtaining means (30, S61, S64, S77, S92) for obtaining acceleration data (Da) which is output from the acceleration sensor; rotation motion determination means for determining a rotation motion of the input device around a predetermined direction as a rotation axis, by comparing a start point (Ps) in a two-dimensional coordinate system which is defined by the first acceleration data obtained in a predetermined period, and an end point (Pe) in the two-dimensional coordinate system which is defined by the last acceleration data obtained in the predetermined period, wherein the coordinate axes (X, Y) of the two-dimensional coordinate system correspond to the two axial directions of the acceleration data, and the origin of the two-dimensional coordinate system represents a value of the acceleration data in the state where no acceleration including the acceleration of gravity acts upon the acceleration sensor; the rotation motion determination means including: angle calculation means (30, S101) for calculating an angle (Θ) enclosed by a line segment from the origin toward the start point (Ps) in the two-dimensional coordinate system and a line segment from the origin toward the end point (Pe) in the two-dimensional coordinate system; rotation direction determination means (30, S102) for, when the angle (Θ) exceeds a first threshold value, determining that the input device has been moved while being rotated in one of two directions, and when the angle (Θ) is less than a second threshold value, determining that the input device has been moved while being rotated in the other of the two directions with respect to the rotation axis; and output means (30, S102, S106) for outputting motion data (Dj) including at least the rotation motion determined by the rotation motion determination means based on the angle (Θ) and the rotation direction determined by the rotation direction determination means. data obtaining means (30, S61, S64, S77, S92) for obtaining acceleration data (Da) which is output from the acceleration sensor; rotation motion determination means for determining a rotation motion of the input device around a predetermined direction as a rotation axis, by comparing a start point (Ps) in a two-dimensional coordinate system which is defined by the first acceleration data obtained in a predetermined period, and an end point (Pe) in the two-dimensional coordinate system which is defined by the last acceleration data obtained in the predetermined period, wherein the coordinate axes (X, Y) of the two-dimensional coordinate system correspond to the two axial directions of the acceleration data, and the origin of the two-dimensional coordinate system represents a value of the acceleration data in the state where no acceleration including the acceleration of gravity acts upon the acceleration sensor; the rotation motion determination means including: angle calculation means (30, S101) for calculating an angle (Θ) enclosed by a line segment from the origin toward the start point (Ps) in the two-dimensional coordinate system and a line segment from the origin toward the end point (Pe) in the two-dimensional coordinate system; rotation direction determination means (30, S102) for, when the angle (Θ) exceeds a first threshold value, determining that the input device has been moved while being rotated in one of two directions, and when the angle (Θ) is less than a second threshold value, determining that the input device has been moved while being rotated in the other of the two directions with respect to the rotation axis; and output means (30, S102, S106) for outputting motion data (Dj) including at least the rotation motion determined by the rotation motion determination means based on the angle (Θ) and the rotation direction determined by the rotation direction determination means. angle calculation means (30, S101) for calculating an angle (Θ) enclosed by a line segment from the origin toward the start point (Ps) in the two-dimensional coordinate system and a line segment from the origin toward the end point (Pe) in the two-dimensional coordinate system; rotation direction determination means (30, S102) for, when the angle (Θ) exceeds a first threshold value, determining that the input device has been moved while being rotated in one of two directions, and when the angle (Θ) is less than a second threshold value, determining that the input device has been moved while being rotated in the other of the two directions with respect to the rotation axis; and output means (30, S102, S106) for outputting motion data (Dj) including at least the rotation motion determined by the rotation motion determination means based on the angle (Θ) and the rotation direction determined by the rotation direction determination means.