Abstract: A strut height adjusting apparatus for adjusting the height of a strut automatically and simultaneously to measure the height of a floor while ensuring the perpendicularity of the strut with a warning sound or other indication. The strut height adjusting apparatus includes a light receiving unit for receiving a laser beam for use in setting a hypothetical level which is vertically movably and fitted to a hollow body. A pointer provided for the light receiving unit and a scale plate member indicates the position of the pointer provided for the hollow body. The lower end of a rotary unit is set upright in such a way that it abuts against a base floor to be examined. The light receiving unit is moved up and down so that the laser beam from a laser beam emitter may be received at the center of the light receiving unit. The height of the second floor can be measured by reading graduations on the scale plate member as indicated by the pointer.