PURPOSE: To obtain an apparatus which can execute the apperture synthesis and the difference processing in parallel with the sampling of reflected data in an underground searching radar.

CONSTITUTION: A transmitting antenna 2 obtains the oscillating signal from a pulse oscillator 4 and radiates radio waves into the ground. The radio waves which are reflected from a target 1 are detected with a receiving antenna 3. After the detected signals are amplified with an amplifier 5, the signals are sampled in a sampler 6. The signal is converted into the digital signal with an A/D converter 7. Then, the signal is stored in a reflected signal memory 8 as the reflection data. Reference data are computed before searching and stored in a reference data memory 9. In an operator 10, the correlation between the content of the reflected signal memory 8 and the content of the reference data memory 9 is obtained. The result of the operation is displayed on a display device 11. The processing is executed based on the timing signal from a generator 12 for process timing.