PURPOSE: To stably continue the tracking of a target, by estimating the position of the target and unnecessary wave arriving direction at the time of the next tracking of the target from the memory data of a history data memory part and controlling an adaptation control loop on the basis of the estimation result.

CONSTITUTION: The signal received by each antenna element 1 is detected through a receiving and amplifying part 2 and subsequently converted to a digital signal by an A/D converter 4 to be distributed to each of a plurality of beam forming operation parts 6 by a distributor 5. The signal operated by each of the operation parts 6 having beam formed thereto is guided to a signal processing part 7 to perform the measurement of a mono-pulse. When an unnecessary wave is present, adaptation control is performed by the adaptation control loop of an adaptation control part 8 so as to minimize the unnecessary wave component of the output signal of the operation part 6. From the present and past data of a target and data of an unnecessary wave arriving direction stored in a memory 9, the position of the target at the time of the next tracking of the target is estimated by an estimation operation part 10 and the estimation result is given to the control part 8. Therefore, when the next tracking of the target is started, a beam shape almost becomes the optimum shape and the stable tracking of the target can be continued.