A repeated determination of a magnitude of a change amount vector with respect to a first threshold value is made. When it is determined that the magnitude is equal to or larger than the first threshold value, predetermined processing is executed, a swinging direction in which an input device is swung is calculated, and intersection of the swinging direction with a second threshold value is determined. After it is determined that the change amount vector intersects with the second threshold value, further, whether or not the magnitude of the change amount vector is smaller than a third threshold value is determined. After the magnitude of the change amount vector is determined to be equal to or larger than the first threshold value, the first threshold is not tested again until the magnitude of the change amount vector is smaller than the third threshold value.