A storage medium storing a game program executed by a computer in a game apparatus for executing a game performed based on a motion of an input device, the game program causing the computer to function as: an output data obtaining means (30, S17) for obtaining output data (Da) indicating a reciprocating tilt motion of a body of an input device itself; an output data storing means (30, S17) for storing a history of the output data obtained by the output data obtaining means into a memory; a peak value detecting means (30, S81) for detecting successive extremums of values from the output data history (AccBuffer) stored in the output data storing means; a peak interval calculating means (30, S81) for calculating a time interval between times when the output data indicating the successive extremums have been obtained, based on the detection of the peak value detecting means; a measurement means (30, S81) for measuring an elapsed time which has elapsed since an extremum has been most recently detected by the peak value detecting means until a current time; a game input data calculating means (30, S89, S92) for calculating dynamic tilt (θc) as game input data based on the elapsed time measured by the measurement means and the time interval calculated by the peak interval calculating means; and a game processing means (30, S92, S22) for executing a game process using the game input data calculated by the game input data calculating means, wherein the game input data calculating means sets a cyclic function simulating transition of values indicated by the output data history which vary while successively repeating the maximum value and the minimum value with cyclicality and calculates dynamic tilt by substituting the elapsed time and the time interval into the cyclic function. an output data obtaining means (30, S17) for obtaining output data (Da) indicating a reciprocating tilt motion of a body of an input device itself; an output data storing means (30, S17) for storing a history of the output data obtained by the output data obtaining means into a memory; a peak value detecting means (30, S81) for detecting successive extremums of values from the output data history (AccBuffer) stored in the output data storing means; a peak interval calculating means (30, S81) for calculating a time interval between times when the output data indicating the successive extremums have been obtained, based on the detection of the peak value detecting means; a measurement means (30, S81) for measuring an elapsed time which has elapsed since an extremum has been most recently detected by the peak value detecting means until a current time; a game input data calculating means (30, S89, S92) for calculating dynamic tilt (θc) as game input data based on the elapsed time measured by the measurement means and the time interval calculated by the peak interval calculating means; and a game processing means (30, S92, S22) for executing a game process using the game input data calculated by the game input data calculating means, wherein the game input data calculating means sets a cyclic function simulating transition of values indicated by the output data history which vary while successively repeating the maximum value and the minimum value with cyclicality and calculates dynamic tilt by substituting the elapsed time and the time interval into the cyclic function.