PURPOSE: To detect abnormal approach over a wide range by, when an object or a person precedes a movable shaft and comes into contact with a tension member surrounding the movable shaft, making the tensile force of the tension member cause deformation in a supporting member, and outputting an electric signal according to the deformation.

CONSTITUTION: In a case where a protecting device is executed on the movable shaft 6 of a three dimensional measurement equipment, an upper and a lower supporting member 12 are severally attached to four corners at the upper and the lower end of the movable shaft 6 so as to protrude to the side of the movable shaft 6, and a wire (tension member) 13 is stretchingly provided between the upper and the lower supporting member. When the movable shaft 6 stretches as it moves laterally with a carriage, and is about to come into contact with an object or a person, the wire 13 procedes the movable shaft 6 and comes into contact with the object or person, and tensile force acts on the wire 13. A movable plate (movable electrode) 17 therefore bends upward to open a contact 18 for electrically shutting off an abnormal approach detecting circuit. Thus an abnormal signal is outputted from a signal processing section, and the driving system of the three dimensional measurement equipment is stopped by a command issued from a controller.