A load port adapted for wafer cassettes of different sizes detects storage states of wafers stored in the wafer cassettes. The load port includes a body, a positioning mechanism, a sensing mechanism, and a detecting mechanism. The body has a carrier base. The positioning mechanism is disposed on the body and has a positioning unit disposed on the carrier base, a hooking unit, and a limiting unit. The hooking unit is disposed in the body and has a driving assembly and a hooking element. The driving assembly is disposed in the body. The hooking element is mounted to the driving assembly. The sensing mechanism is disposed on the carrier base. The detecting mechanism is disposed on the body, detects the storage states of wafers stored in the wafer cassette, and has a first detecting assembly and a second detecting assembly spaced apart from each other.