Abstract: A door scope provided in a door for viewing outside from inside includes an optical system consisting of five lenses: a large diameter objective having a concave rear face, two auxiliary objectives having concave rear faces, a biconcave compensation lens and an eyepiece. The compensation lens is located behind the two auxiliary objectives or therebetween. A peep preventing device consisting of two polarizers one of which is made rotatable with respect to the other is attachable to the door scope. The compensation lens is preferably made of glass material different from that of the other lenses to correct chromatic aberration.