To provide a fall preventing device having extremely satisfactory safety with which unlocking is disabled without performing any special operation.

This device has a guide groove 4 for guiding a cable 5 and two flanges 1 and 2 for supporting a shaft 6, to which a lever 7 is attached so as to be turned, a ring bolt hole 8 for fixing a snap hook 9 is provided at one end of the lever 7, a cam 10, which is engaged with the cable 5 for stopping the move of this device along with the cable 5 when a user falls, is provided at the other end, the flanges 1 and 2 can be turned while facing each other so as to move mutually separately and closely in order to position this device on the cable 5 by mutually linking the flanges 1 and 2 through a hinge 3, and a safety means is provided for blocking the opening of the flanges 1 and 2 when the cable 5 is inserted into the guide groove 4 and the lever 7 is not located at a standstill position where the cam 10 is away from the cable 5.