An exposure method for exposing an image of a mask pattern onto a plate via a projection optical system. The method includes a step of illuminating one of a binary mask and an attenuated phase shifting mask, which has a contact hole pattern and an auxiliary pattern, by utilizing light from a light source and an illumination optical system so that the contact hole pattern can be resolved, but a resolution of the auxiliary pattern is restrained. The illuminating step uses an off-axis illumination that is polarized in a tangential direction when a value that is calculated by normalizing half the length of an interval between centers of the auxiliary pattern and the contact hole pattern that are adjacent to each other by .lamda./NA is 0.25.times. {square root over (2)} or smaller, where .lamda. is a wavelength of the light, and NA is a numerical aperture of the projection optical system at an image side.