A direction tracking method is proposed for quickly tracking directions-of-arrival of radio waves even in an environment where trajectories of the directions-of-arrival intersect. With the tracking method, the state vectors of directions-of-arrival (composed of a direction-of-arrival and the angular velocity and acceleration of the direction-of-arrival) at the current direction updating time are predicted with an observer by using state vectors of directions-of-arrival at the previous direction updating time to calculate provisional estimates of the directions-of-arrival, and furthermore, the state vectors at the current direction updating time are calculated based on the provisional estimates, the predicted state vectors, and predicted values of the directions-of-arrival to calculate estimates of the directions-of-arrival from the state vectors.