A game apparatus including an obtaining logic unit, a gravity direction calculating logic unit, a first movement direction calculating logic unit, and a game processing logic unit. The obtaining logic unit successively obtains acceleration data. The gravity direction calculating logic unit calculates a gravity direction based on values of a plurality of pieces of acceleration data obtained during a predetermined period, where an orientation of an input device is used as a reference. The first movement direction calculating logic unit calculates a first movement direction which is a movement direction of the input device, based on the values of the plurality of pieces of acceleration data obtained during the predetermined period, where the orientation of the input device is used as a reference. The game processing logic unit executes a game process based on the first movement direction and the gravity direction.