NORMAL DETECTION METHOD, NORMAL DETECTION DEVICE, AND MACHINING MACHINE PROVIDED WITH NORMAL DETECTION FUNCTION

A normal detection method for measuring the distance to a measurement subject (20) using one or more distance detectors (30), and obtaining a normal vector (Vn) on the measured surface (21) of the measurement subject (20) from the obtained measurement result (L), wherein: within a three-dimensional space, the straight line linking a first measurement point (Qa) measured at a first measurement position (Pa) using the distance detector (30) and a second measurement point (Qd) measured at a second measurement position (Pd) different from the first measurement position (Pa) is set as a first vector (Vad); the straight line linking the first measurement point (Qa) and a third measurement point (Qf) measured at a third measurement position (Pf) different from the first measurement position (Pa) and the second measurement position (Pd) as a second vector (Vaf); and a normal vector (Vn) on the measured surface (21) is obtained by determining the vector product of the first vector (Vad) and the second vector (Vaf).