To provide a safety device for an elevated job site in which safety is improved by preventing a master rope from being considerably loosened when blocking the fall of a worker.

A hook 2 provided on one terminal of a master rope 1 is engaged to an engage object A, the other terminal is inserted into a master rope tension device 10 locked on the engage object A, and the master rope 1 is kept tense by the engagement of an engage pawl 14. A rope stopper 20 is freely attachably and detachably mounted on the portion of the master rope 1 pulled out of the master rope tension device 10 and when slippage occurs on the engaging part of the master rope 1 and the engage pawl 14 in the case of blocking the fall of the worker, the rope stopper 20 is immediately locked to the master rope tension device 10 so that the master rope 1 can be prevented from being loosened and the worker can be prevented from falling by a large distance.