To enhance detection performance in detecting a living thing by using a microwave.

A microwave sensor 1 quadrature-detects a reception signal vr by using a phase difference between a transmission signal vt and the reception signal vr obtained as a result of its being reflected by the living thing 22, thereby outputting quadrature detection output signals (signals vi and vg). The output signals are supplied as signals I and Q to a noise processing part 5 via an amplification/filter part 2 and a noise processing determination part 3. The processing part 5 executes noise processing with respect to noise components in phase with or in opposite phase to one signal of the two signals comprising the output signals by utilizing the signals I and Q. This provides a signal vm with noise pre-processed. A detection/determination processing part 6 detects the living thing 22 by utilizing the signal vm with the noise pre-processed. This detector can be applied to a food-eating harmful insect detector that utilizes a microwave sensor.