A coupling tool being used while closing a hook portion and arranged to prevent such a trouble as the hook portion is opened by mistake by some chance to cause uncoupling. In the coupling tool where a clearance is formed between the forward end face (25a) of a slide bar (25) and the forward end face (11a) of a hook portion (11) by sliding a grasping portion (26) along a guide groove (23) while projecting to the outside of the guide groove (23), a lock groove (31) is branched from the guide groove (23) such that the grasping portion (26) can move to the lock groove (31), the forward end face (25a) of the slide bar (25) is abutted against the forward end face (11a) of a hook portion (11) by an urge member (24) under a state where the grasping portion (26) is entering the lock groove (31), and axial movement of the slide bar (25) is limited through contact of the lock groove (31) and the grasping portion (26) thus preventing the clearance from widening.
