An optical body height measurement instrument is provided comprising: a lens configured to be movable along a direction parallel to the height of an object to be measured and form an image of the object; a photosensitive sensor arranged at an image side of the lens to sense the image; and a driving device configured to drive the lens along a direction parallel to the height of the object, wherein when the lens is moved across the height at which the head of the object is located, a hop occurs to an output of the photosensitive sensor; and wherein the height of the object is determined based on the height of the lens measured at the time of the occurrence of the hop. The optical body height measurement instrument can rapidly, conveniently and accurately measure the height based on the infrared rays emitted from the measured object or the light with a predetermined wavelength emitted from an auxiliary light source so long as the person to be measured stands within a certain region.