An optical unit assembly is provided with an optical system including an optical component for irradiating a target object with light and receiving the reflected light, a casing for accommodating the optical system, a supporting frame for supporting a part of the casing, and a height adjusting member having a supporting surface for supporting another part of the casing and placed between the supporting frame and the casing. The height adjusting mechanism is slidable between the supporting frame and the casing with a supported state of the casing by the supporting frame substantially maintained, and the supporting surface includes at least a first supporting surface set at a specified first height position and a second supporting surface set at a second height position different from the first height position.