To provide a non-contact type detector for detecting a position of a thread groove capable of directly detecting the position of the thread groove and never lowering measuring precision even in repeatedly measuring it and a machine tool.

A laser beam emitting means 71 and a laser beam receiving means 72 relatively positioned are set so that a distance from an optical axis of a laser beam to a workpiece rotation axis CZ becomes longer than a distance from the workpiece rotation axis to a bottom part BN of the thread groove and shorter than a distance from the workpiece rotation axis to a top part TN of the thread groove and set at an angle corresponding to a pitch of the thread groove against the workpiece rotation axis so that the optical axis of the laser beam comes to be in parallel with the thread groove at a measurement point of the workpiece. Thereafter, a position in the lead direction on the thread groove is detected based on a detection signal taken up from the laser beam receiving means, while relatively moving the laser beam emitting means and the laser beam receiving means which are relatively positioned, against the workpiece in the lead direction of the thread groove, or while rotating the workpiece around the workpiece rotation axis.