Abstract: A passive optical switch for an automatic door for opening and closing a door comprises a light receiving portion provided with a segmented light receiving surface formed by a number of the optical fiber fluxes so as to be adjusted to the focus of a lens, a phototube cell converter portion connected to each of the optical fiber fluxes extending from said light receiving portion, a voltage change detecting portion for detecting the change of an output of said phototube cell converter portion and a direction discriminator circuit for analyzing a detecting signal emitted from said voltage change detecting portion, whereby an automatic opening and closing of a door may be effected by discriminating onward movement of a passing body by detecting the change of an output emitted from said phototube cell converter portion caused by a passing body.