PURPOSE: To choose only living ticks and to count these ticks without dyeing them by performing the subtraction between an image that is not physically stimulated yet and an image that is already stimulated against the test samples including the living ticks.

CONSTITUTION: The images are fetched from a CCD camera controller 1 by an image fetching device 10 and stored in am image storage 11. Meanwhile a stimulation command is sent to a physical stimulation controller 8 from a physical stimulation command device 12. Thus the physical stimuli are given to the test samples so that the living ticks have motions. The images of moving ticks are fetched by an image fetching device 13 through a CCD camera controller 7 and then stored in an image storage 14. Then an inter-image arithmetic unit 15 applies the arithmetic operations to the images stored in both storages 11 and 14 and extracts only the images of living ticks. These images are sent to a binarizing device 16 where the images (living ticks) are separated from the background, and a counter device 17 counts the images (living ticks).