To precisely calculate a gravity direction, even when an input device is moving.

The gravity direction calculation device includes an acquisition means, a duration detection means, and a gravity direction calculation means. The acquisition means sequentially acquires acceleration data, output from a multi-axis acceleration sensor mounted on an input device. The duration detection means detects duration, since the input device started to move until the motion ends as moving duration, on the basis of the acquired acceleration data. The gravity direction calculation means calculates the total sum of one or more acceleration vectors, corresponding to one or more acceleration data acquired within the moving duration and sets the direction, determined by the vector indicated by the summation, as the gravity direction, wherein the acceleration vector is the vector of which the components are acceleration values, with respect to a plurality of axes from among the acceleration values with respect to respective axes indicated by the acceleration data.

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