Three-dimensional measuring device

A three-dimensional measurement device is provided with: a light source unit that emits distance measurement light; a projection optical unit that irradiates distance measurement light onto the distance measurement optical axis; a scanning mirror that is provided so as to be rotatable about the rotation axis while being inclined with respect to the axis of the rotation axis, and that rotatably irradiates the distance measurement light within a plane intersecting the rotation axis; a light receiving optical unit that receives the reflected distance measurement light; a reference light optical unit that is provided in a range other than the measurement range in the irradiation range, receives and reflects the distance measurement light reflected by the scanning mirror as internal reference light, and is capable of changing the light amount of the reflected internal reference light; and a light receiving element that receives the reflected distance measurement light and the internal reference light guided from t