To improve accuracy of walking navigation by autonomous navigation.

Acceleration data is acquired in discrete time in an arbitrary segment from a three dimensional acceleration sensor for outputting data indicating a composite vector of gravity and inertia force acting on unit mass as acceleration data, the horizontal component and vertical axis component of the acceleration of the three-dimensional acceleration sensor are derived based on the acceleration data, the tilting of the horizontal vibration axis as the longitudinal axis of the distribution of the horizontal component of the acceleration with reference to the tilting of the posture of the three-dimensional acceleration sensor is derived by statistical operation, and one of two directions parallel to the horizontal vibration axis is determined as a walking direction with reference to the posture of the three-dimensional acceleration sensor in the arbitrary segment, based on the shift between the vibration phase of the horizontal vibration axis component of the acceleration and the vibration phase of the vertical axis component of the acceleration.