To provide a manufacturing method of a phase difference element which is superior in moisture resistance. After forming an optically anisotropic layer by way of oblique vapor deposition on a substrate, the optically anisotropic layer is covered by a protective layer made by depositing an inorganic compound by way of an atomic layer deposition method. More specifically, established is a manufacturing method of a phase difference element containing a transparent substrate, optically anisotropic layer containing a birefringent film and a protective layer, the method including: an optically anisotropic layer formation step of forming an optically anisotropic layer by forming a birefringent film by way of oblique vapor deposition; and a protective layer formation step of forming a protective layer by depositing an inorganic compound by way of an atomic layer deposition method.