The present invention provides a safety unit comprising: a case; a rotary linkage disposed at one end thereof at the outside of the case and rotatably mounted at the other end thereof to the case; a force transfer shaft mounted to one side of the rotary linkage in such a fashion as to be oriented perpendicular to the rotating plane of the rotary linkage; a crank linkage rotatably mounted at one end thereof to the inner side of the case and adapted to abut against the force transfer shaft at the outer circumferential edge thereof so as to be transferred with an external force to be rotatably moved; and a support means rotatably connected to the other end of the crank linkage and adapted to allow for the rotation of the crank linkage when an external force having a value larger than a predetermined threshold value is exerted to the rotary linkage.
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