Abstract: At least a part of a periphery of a liquid storage tank is submerged in water. A leakage inspection apparatus has a depressurizing device that depressurizes the inside of the liquid storage tank. The apparatus includes a rod part inserted in the liquid storage tank. A float is fitted with the rod part such that it floats on the surface of the liquid in the storage tank and moves along the rod part in accordance with displacement of the liquid surface. A moving magnet is provided in the float, and a reference magnet is fixed at a lower portion of the rod part. A body part detects the position of each of the moving magnet and the reference magnet, and a measuring device determines the position of the moving magnet relative to the reference magnet in accordance with a signal from the body part.