PURPOSE: To obtain a small walking animal detector which can identify a small walking animal quantitatively at all times.

CONSTITUTION: When a small animal walks on a printed board formed with a pair of interdigital conductors 1a, 1b specifically spaced apart from each other and comes into contact with the conductors 1a, 1b, capacitance of the printed board 1 varies. The variation is transmitted through a node 3e to a bridge circuit 3 where imbalance takes place to produce difference between AC signals at nodes 3e and 3f. The differential component is amplified through an AC differential amplifying circuit 4 and transmitted, as a differential signal, to a detecting circuit 5. The detecting circuit 5 detects the differential signal and produces a detection signal which is then compared with a reference voltage at a voltage comparator circuit 7 and an 'H' level detection signal is produced therefrom. A pulse generating circuit 8 detects rising of the detection signal from 'L' level to 'H' level and produces a single pulse.