Abstract: The entrance security door apparatus has the object of providing security for the receiver in a condominium, etc., when the receiver must confirm an unexpected visitor, etc., by opening and closing a door such as entrance door. A locking tool is provided so that the door can be opened and closed to the side end side of a door opening frame, wherein the security door apparatus comprises: one side end part of an auxiliary door having a predetermined narrow width is connected to the inner side of the open/close side of the door and the other side end part of the auxiliary door is connected to the inner part of the side end of the open/close side of the door opening frame, and the auxiliary door is linked in such a manner that. When the door is opened, the auxiliary door functions as a barrier in the opening part between the door and the door opening frame. The auxiliary door is formed to have a lattice-shape shape, etc., so that the receiver can visually confirm the outside from the interior.