PURPOSE: To detect an error in its early stages due to a defective control of probes, etc., and hence to cope with it without wasting time by providing a means for detecting abnormality on the side of the probes which are relatively moved.

CONSTITUTION: A displacement amt. of a cantilever 22 in each of (x)-(z) directions expected by a transmitted control voltage for each of three- dimensional driving mechanisms is calculated by a microcomputer 1, and this is compared with an actual displacement amt. detected by each corresponding cantilever displacement amt. detecting means 25. Then, when this difference is more than a prescribed value, it is decided that this three-dimensional driving mechanism is deffective to make an error. As a result of this decision, one of the plural three-dimensional mechanisms inflicted with abnormality is displayed at a display by the microcomputer 1. Thus, it is possible to cope with an error by finding it in its early stages.