A gravity direction calculating apparatus for calculating a direction of gravity with respect to an input device, including: an obtaining logic unit for successively obtaining acceleration data output from a multi-axis acceleration sensor included in the input device; a period detecting logic unit for detecting a period from start to end of movement of the input device, as a movement period, based on the obtained acceleration data; and a gravity direction calculating logic unit for calculating a sum of one or more acceleration vectors corresponding to one or more pieces of acceleration data obtained during the movement period, a direction determined by a vector indicated by the sum being the gravity direction, wherein the acceleration vector is a vector whose components are acceleration values with respect to a plurality of axes of acceleration values with respect to axes indicated by the acceleration data.