Provided is a velocity calculating apparatus including: a horizontal-angular-velocity-detecting portion disposed to a main-body portion attached to a movable object moving along a movement plane to detect a horizontal-axis angular velocity around a horizontal axis perpendicular to a moving direction generated according to an inclination angle of the movement plane; a vertical-acceleration-detecting portion disposed to the main-body portion to detect a vertical acceleration generated according to a shape of the movement plane; a time-difference-calculating portion configured to calculate a time difference between characteristic components occurring in the horizontal-axis angular velocity and the vertical acceleration due to a position of the movement plane; and a velocity-calculating portion configured to calculate a time-differential velocity based on a ratio between an installation distance from a position to which the horizontal angular velocity is exerted in the overall movable object to an installation position of the main body portion and the time difference.