This invention provides an optical measurement device enabling a highly accurate measurement with respect to a measuring target object in which an inclined surface or a curved surface exists at one part of the surface or a tilted measuring target object. The light shielding portion is configured to define an incident angle range with respect to a light receiving center axis of a diffuse reflected light. In other words, a maximum angle formed by the advancing direction of the diffuse reflected light and the light receiving center axis when the diffuse reflected light passes through the opening of the light shielding portion is defined by the diameter of the opening. The light projecting portion projects a light projection beam so that a converging position on the light receiving center axis is included within a range of the light shielding portion on the light receiving center axis for the component converged by the lens portion of the light projection beam (i.e., reflected light beam) specular reflected at the surface of the measuring target object.