We have developed a noncontact-type relative displacement sensor for structural health monitoring which is capable of measuring relative displacement and rotation angle of the object independently. The sensor is composed of a laser as a measurement target and two position sensitive detectors (PSDs). The accuracy of the sensor system was experimentally evaluated to be 0.10 mm in the relative displacement measurement and 0.22 mrad in the rotation angle measurement respectively. These results indicate that the developed sensor system has a sufficient accuracy for structural health monitoring.