A three-dimensional measurement device includes: an illuminator that irradiates a measured object with a predetermined light; an imaging device that comprises: an imaging sensor displaceable at least in a vertical direction; and a both-sided telecentric optical system that causes the imaging sensor to form an image of a predetermined area on the measured object irradiated with the predetermined light; a conveyor that moves the illuminator and the imaging device relative to the measured object; and a controller that: executes three-dimensional measurement of a predetermined measurement object on the measured object, based on the taken image; measures a height of the predetermined area at least at a time prior to imaging of the predetermined area under the predetermined light; and changes a height position of the imaging sensor based on a measurement result to adjust an interval between the predetermined area and the imaging sensor to a predetermined distance.