A velocity calculating apparatus, comprising: a horizontal angular velocity detecting portion configured to be disposed on a main body portion attached to a movable object moving along a movement plane and configured to detect a horizontal axis angular velocity (ω y), wherein said horizontal axis angular velocity is an angular velocity around a horizontal axis (y) perpendicular to a moving direction of the movable object generated according to an inclination angle of the movement plane; wherein said movement plane has some degree of unevenness; a vertical acceleration detecting portion disposed on the main body portion and configured to detect a vertical acceleration (α z), wherein said vertical acceleration is an acceleration in the vertical direction (z) generated according to a shape of the movement plane; a time difference calculating portion configured to calculate a time difference (ΔT) between a characteristic component occurring in the horizontal axis angular velocity (ω y) and a characteristic component occurring in the vertical acceleration (α z) due to a predetermined position of the movement plane; the velocity calculating apparatus characterized in that it further comprises: a velocity calculating portion configured to calculate a time differential velocity VT representing a velocity in the moving direction of the movable object based on a ratio between an installation distance D from a position to which the horizontal axis angular velocity is estimated to be exerted in the overall movable object to an installation position of the main body portion and the time difference ΔT according to VT=D/ ΔT, wherein the velocity calculating apparatus is configured to be installed at a front side of the movable object, a central position or a rear side. a horizontal angular velocity detecting portion configured to be disposed on a main body portion attached to a movable object moving along a movement plane and configured to detect a horizontal axis angular velocity (ω y), wherein said horizontal axis angular velocity is an angular velocity around a horizontal axis (y) perpendicular to a moving direction of the movable object generated according to an inclination angle of the movement plane; wherein said movement plane has some degree of unevenness; a vertical acceleration detecting portion disposed on the main body portion and configured to detect a vertical acceleration (α z), wherein said vertical acceleration is an acceleration in the vertical direction (z) generated according to a shape of the movement plane; a time difference calculating portion configured to calculate a time difference (ΔT) between a characteristic component occurring in the horizontal axis angular velocity (ω y) and a characteristic component occurring in the vertical acceleration (α z) due to a predetermined position of the movement plane; the velocity calculating apparatus characterized in that it further comprises: a velocity calculating portion configured to calculate a time differential velocity VT representing a velocity in the moving direction of the movable object based on a ratio between an installation distance D from a position to which the horizontal axis angular velocity is estimated to be exerted in the overall movable object to an installation position of the main body portion and the time difference ΔT according to VT=D/ ΔT, wherein the velocity calculating apparatus is configured to be installed at a front side of the movable object, a central position or a rear side. a velocity calculating portion configured to calculate a time differential velocity VT representing a velocity in the moving direction of the movable object based on a ratio between an installation distance D from a position to which the horizontal axis angular velocity is estimated to be exerted in the overall movable object to an installation position of the main body portion and the time difference ΔT according to VT=D/ ΔT, wherein the velocity calculating apparatus is configured to be installed at a front side of the movable object, a central position or a rear side.