To minimize the generation of erroneous alarms by deciding that whether or not the property of a target detected by signals from an oscillator and the output of a mixer stage can become sufficient bases for triggering an alarm instruction.

The outputs of an oscillator and mixer stage are sent to a buffer memory 40 through a converting means 30. A coefficient from the buffer 40 is sent to one input of a pattern recognizing means 50 and, at the same time, a coefficient stored in the first area 60-1 of a template storage device 60 is sent to the other input of the means 50. Then comparison is performed for a first template and, when no matching is established, the content of the second template area 60-2 of the device 60 is sent to the second input of the means 50 and the comparison is again made. Then an output signal indicating whether or not the specific template matches an arriving buffer coefficient is provided. Simultaneously, the content of the second area 70-2 of a discriminating and storing device 70 is sent to an alarm gate means and an alarm triggering function is enabled or disabled.