I will explain how we can distinguish the gravitational lensing of dressed black holes (BHs), which have large dark matter halos surrounding them, from that of bare BHs with gravitational wave (GW) diffraction. In the search for BHs using gravitational lensing, distinguishing dressed BHs is crucial because they can provide evidence of primordial BHs. GW diffraction allows us to differentiate them by observing differences in the gravitational lensing patterns in the low-frequency range. In observations with ground-based GW detectors, we expect that GW diffraction will play a crucial role in identifying dressed BHs with central BH masses below 100 solar masses. Thus, this method can help determine the origins of BHs currently detected by LIGO.