Abstract: A touch sensor is disclosed which is capable of readily and precisely aligning the center of working shaft of a machine tool with that of a measuring element and allowing the distal end of the element to move in a wide range in the three-dimensional directions. The touch sensor includes a plurality of adjusting screws which extend through a casing and are forcedly pressed at one end thereof against a cylinder rotatably receiving a steel ball of the measuring element therein to remove a gap of a micro-distance between the cylinder and the steel ball formed during the assembling to render fine adjustment of the measuring element possible, to thereby precisely carry out the centering of the element.