An image sensing apparatus has a cut-off characteristic which is changed by a mechanism for rotating a simple optical low-pass filter having a tightly sealed structure about the periphery of the photographic optical path. Light from a lens representing a subject is received and converted by an image sensing unit upon having its high-frequency components attenuated by a suitable cut-off characteristic, which is for obtaining a color natural image, of a stacked member including an optical low-pass filter or birefringence plates constructing an optical low-pass filter. In a case where a monochromatic image is obtained, some or all of the birefringence plates are rotated through a predetermined angle by changeover means such as a transmission member without sacrificing the seal about the periphery of the optical path, thereby changing over the cut-off characteristic of the optical low-pass filter to a cut-off characteristic suitable for obtaining a monochromatic image. The light from the subject is then received and converted by the image sensing unit.