A three-dimensional measurement system using an IGPS includes a rescale bar having linear scales thereon, a linear encoder for measuring an absolute length within which the linear encoder moves on the rescale bar, a plurality of optical transmitters that radiates pan beams, and a vector bar having one end attached to the linear encoder, and having a receiver to detect the pan beams radiated from the optical transmitters, the vector bar acquiring coordinates of two points where the vector bar moves by using the receiver, and measuring a relative length from the coordinates. A ratio between the absolute length and the relative length is applied in rescaling an actual distance between two positions to be measured.