There is provided a safety door having a rotary body hinged to a door frame and a slider overlapping with an end of the rotary body. The safety door includes a fastening portion provided on at least one surface of an overlapping region of the rotary body and the slider, thus preventing separation and deformation of the overlapping region and guiding a movement of the slider, and a stopper preventing the slider from being removed from the rotary body and fixing or restricting a position of the slider. The rotary body and the slider decrease a width of a door by an overlapping movement of a female guide groove and a male protrusion. The safety door further includes a resilient pad provided between the protrusion and the guide groove and supporting an impact generated by a reduction in the width of the door.
