To improve the measurement performance of the surface height in a workpiece by wavelength light focused on the workpiece in which the treatment of the white light color to be used is facilitated.

The laser beam machining device includes a detection means 10 where white color light emitted from a white color light source 101 is introduced into a second condensing lens 102 using a first optical fiber 103 so as to be condensed on a workpiece W, and the reflected light from the workpiece W is introduced into a detector 110 detecting the intensity of the reflected light using a second optical fiber 120, the treatment of the while color light used for condensing and emitting to the workpiece W is facilitated, and also, the stable propagation only of the wavelength light which is focused on the workpiece W is performed.