The present invention provides a method of manufacturing an ND filter having a gradation density distribution, the ND filter, and an aperture device and a camera having the ND filter. A structure thereof is as follows. The method of manufacturing an ND filter having at least two kinds of films on a substrate includes the steps of: forming a film of at least one layer other than an outermost layer having a gradation density distribution while rotating a slit mask integrally with the substrate; and forming a film of the outermost layer without using the slit mask.