A method of measuring a three-dimensional position of a workpiece by using a laser measuring unit provided at a hand portion of an industrial robot, the laser measuring unit including an image recognition camera and first and second laser beam sources for emitting lateral and vertical slit beams, respectively, the method comprising the steps of: positioning the laser measuring unit such that the laser measuring unit confronts the workpiece; emitting the lateral and vertical slit beams towards the workpiece from the first and second laser beam sources, respectively; inputting the lateral and vertical slit beams on the workpiece, as first and second slit images, into the image recognition camera, respectively; detecting a first point of a maximum output of the lateral slit beam at an edge of the workpiece in the first slit image and a second point of a maximum output of the vertical slit beam at another edge of the workpiece in the second slit image; and calculating the three-dimensional position of the workpiece based on a first amount of deviation of the first point from a first preset reference point and a second amount of deviation of the second point from a second preset reference point.