To realize by far effective impact absorption during block of rotation by improving a drop preventing device to effect block of rotation through locking in various elevating devices.

The drop preventing device is constituted such that a claw member (6) operated based on a centrifugal force is supported at a rotor (2); the claw member (6) is locked with a lock part (7b) of a stator (4) when the rotor (2) exceeds the fixed number of revolutions and blocks rotation of the rotor (2); and in this case, the claw member (6) is worked on a braking element (8); the braking element (8) is plastically deformed in a rotation block process for preventing a drop and is constituted to absorb its impact; and the braking element (8) is situated in a chamber.