PURPOSE: To ensure the operation of a probe and to simplify the mechanism thereof, by converting the displacement of the axis of the probe due to a touch into a change in the intensity of the light of an optical fiber, and by detecting the touch from this change.

CONSTITUTION: When the main body 1 of a case is moved upward in the figure, the contact 5 of a probe axis 2 touches an object W, and thereby the axis 2 is rotated counterclockwise around a pin 7 as a supporting point. Then the pressing part 6 of the axis 2 is rotated toward a guide pin 10, and an optical fiber 9 is pressed and deformed by the pressing part 6 and the pin 10. when the fiber 9 is deformed, a transmitted light decreases and an output of a photoelectric transducer 17 lowers. When this output falls down to a reference voltage Vref, a detection signal is output from a comparator 22, and thereby the touch of the contact with the object W is detected.