A displacement measurement device 10 is provided with: a laser light source 11 for emitting laser light to a measurement area R of a measurement target object S; a focusing optical system (the beam splitter 151, the first reflecting mirror 1521, the condenser lens 155) having a front focal point in the measurement area R and a rear focal point on a predetermined imaging surface (the detection surface 1561); a non-focusing optical system (the beam splitter 151, the diffuser 153, the second reflecting mirror 1522, and the condenser lens 155) in which light from a measurement area R of a correspondence point in the measurement area corresponding to each point of the imaging surface with respect to the focusing optical system is incident on the point of the imaging surface; and a photodetector (image sensor 156) configured to detect light intensity on the imaging surface for each point. Thus, corresponding to each of a large number of points in the measurement area R, main reflected light reflected at the point and reference light reflected at the surrounding range of the point are incident on each of a large number of points in the imaging surface, and the main reflected light and the reference light interfere at a large number of points in the imaging surface. Thus, an interference pattern is obtained.