PURPOSE: To enable continuous tracking of a target overcoming temporary missing thereof by performing a servo control based on a error angle detection signal or that held according to the level of electromagnetic waves being received.

CONSTITUTION: An error angle detection signal between the axis of an antenna 3 and the coming direction of an electromagnetic wave 1 with a phase detector 6 is applied to a servo amplifier 9 via a hold circuit 8 to track a target by a servo control of the axis of an antenna 3. This hold circuit 8 is enabled when the reception level is below a specified value through a reception level detector 7 and the servo control is performed based on a hold value of the circuit 8 until the reception level exceeds the specified value. This enables the continuous tracking of the target even when it is missed temporarily.