An apparatus for depositing a mono-molecular layer on a substrate surface comprises first and second containers which contain a liquid and are connected via a connecting passage, and a pressure applying mechanism for applying pressure on the liquid in the second container. A mono-molecular layer is formed at the liquid surface of the liquid in the first container, and the mono-molecular layer is deposited on the substrate surface by controlling the pressure applying mechanism so that the liquid surface of the first container rises and falls with respect to the substrate which is essentially stationary.