PURPOSE: To make a stylus detectable and adjustable in an easy manner even if it is installed in a state of eccentricity, by setting a clamp, arranged with three clamp screws radially, concentrically to a tracer head free of rotation.

CONSTITUTION: A pair of rolling bearings 9 and 9 are fitted in the circumference of a shaft part 8 at the tip end of a tracer head 4 as sandwiching a bush 10, while slipperiness in these bearings 9 and 9 is locked tight by a cover plate 12 being bolted 11 to the end of the shaft part 8. A cylindrical part 4 of a clamp 13 is fitly installed in each circumference of these bearings 9 and 9, while the clamp 13 is concentrically set to a tracer head 4 free of rotation. The clamp 13 is radially arranged with three clamp screws 17 around a setting hole 16 in which a stylus 5 pierces through, at regular intervals. When the stylus 5 is somewhat eccentric, a dial gauge pointer moves so that adjustment should be done till a gauge 18 will no longer move with these screws 17 adjusted.