To obtain a protective door formed in a solid state, and perform safe and smooth opening and closing by a method wherein a spring body is suspended from the lower ends of a plurality of suspension members, adjoining panels are intercoupled through a hinge to constitute a door opening and closing in a bellows-form manner, an engaging lever is protruded from the upper end of each panel body, and the forced spreading angle of the hinge is regulated to a value lower than a specified value under a door full opening state.

A panel is suspended from the lower ends of a plurality of suspension members and the adjoining panel bodies are coupled together through a hinge 5. An engaging lever engaged with the side of a beam part is protruded from the upper end of each panel body. The hinge 5 is constituted such that a pair of vane pieces 51 are rotatable through a common pivot 50. Since the engaging lever is stretched to a position right above each vane piece 51, a forced spreading angle R between the vane pieces 51 is not opened to 180° or more through engagement of the engaging lever with an upper beam 10, and when an opening closing froce F is executed from a lateral direction, each panel body is smoothly rotated in a folding direction (f).