To provide a configuration at a low cost, capable of surely preventing separation to an unprepared external force without damaging a simple attachment detachment characteristic, and having high versatility.

A safety hook 1 is configured such that one edge 4a of a closing body 4 is pivotally supported by a spindle 8 in a swingable manner to a base part 2a of a hook-shaped hook part 2. The closing body 4 is formed by two side plates 4c oppositely arranged so as to put the base part 2a between, and a connection part 4d connecting the side plates 4c to each other on a rotational direction outside. A slot 5 is curved on each of the side plates 4c so as to protrude inwardly in a rotational direction, and the vicinity of the spindle 8 of the slot 5 is bent outwardly in a rotational direction. The slot 5 is arranged slidably with a slide pin 6, and the periphery of the spindle 8 is provided with a coil spring 10 energizing the closing body 4 to a closing direction. In the coil spring 10, a portion between a contact edge 10a contacting the base part 2a and the spindle 8 is formed in a mountain-like shape to the inside, and the crown part of the mountain-like shape projects to a bent part 5a of the slot 5.