A laser straight ruler having a main body and a beam scanner installed on the main body. A laser beam is scanned to form a beam spot on an object. A position sensing device receives a laser beam reflected by the object and senses a position of the beam spot. A signal processing unit drives the beam scanner and processes a signal of the position sensing device. A display displays a change in a distance between the main body and the object and data including a measured distance value from the signal processing unit. An input portion inputs data including adjustment of a scanning width of the beam spot and sets start and end positions of the measured distance. A straight distance of the object is measured or the beam spot having a scanning width corresponding to a measured distance or a predetermined distance is projected to the object.