DESCRIZIONE
A liquid tank, a viewing device for under-liquid observation, and an optical film are disclosed, each excellent in visibility and durability and being easy to clean. In at least one embodiment of the present invention is directed to a liquid tank having a transparent wall, including, on an internal surface of the wall, a first moth-eye layer having a moth-eye structure, and a protective layer covering the moth-eye structure, in this order from the wall side, and preferably, further including, on an external surface of the wall, a second moth-eye layer having a moth-eye structure, and the second moth-eye layer being disposed in a region facing the first moth-eye layer.