PURPOSE: To change a posture easily and to omit the check of an original point by forming a contact so that the end of the contact is always positioned on the turning axial line of the 2nd member fitted freely turnably to the 1st member and its direction is changed.

CONSTITUTION: At the time of measurement, the member 33 is depressed down- wards against a spring 41 and rotated, so that the contact end 46 of the contact 32 is rectangularly opposed to the measuring surface of the substance W to be measured. If an operator removes his hand from the member 33, the member 33 is restored upwards by the spring 41 and fixed so as to be engaged with a taper axis 38. Consequently, the contact end 46 of the contact 32 is located again on a fixed position on the turning axial line L1 of the member 33. Even if the member 33 is turned and the direction of the contact 32 to the substance W to be measured is changed, the contact end 46 of the contact 32 is always located on the fixed position on the turning axial line L1 of the member 33. Consequently, relative displacement of respective displacement detectors detecting the moving extents of the X, Y and Z directions is not generated and the checking work of the original point can be omitted.