A method of correcting a measurement value of a laser scanner includes: in a laser scanner including a light emitting unit, a light receiving unit, a distance measuring unit, an optical axis deflecting unit having at least a pair of prisms deflecting a distance measuring light and a reflected distance measuring light, and an emitting direction detecting unit detecting a deflection angle and an emitting direction of the distance measuring light from the optical axis deflecting unit, (a) measuring a distance to a measurement point, (b) detecting rotation angles of the prisms, and (c) obtaining, based on rotation angles of the prisms, a true distance measurement value corrected for a length of an optical path length difference in light emission and/or light reception caused according to the rotation angles of the prisms by subtracting the optical path length difference from a distance measurement value of the distance measuring unit.