To provide a counter counting a living matter such as a fish hard to count.

A counter 10 includes a tube body 12 being a guide through which the fish passes; an oscillator 14 to oscillate a high-frequency voltage; a detection electrode 16 which is disposed on an outer periphery of the tube body 12 and to which a voltage from the oscillator 14 is applied; a ground electrode 18 disposed on the outer periphery of the tube body 12 and disposed parallel to the detection electrode 16; a detection circuit 20 detecting an electric potential of the detection electrode 16; and a count part 22 counting by variations in electric potential detected by the detection circuit 20. When the fish passes through the tube body 12, the electric potential of the detection electrode 16 is changed and the count part 22 detects the variations in its electric potential and counts the number of fishes.