To solve a problem in a conventional safely verification system which determines that there is no worker by mistake to make a machine start operating against the existance of a worker in an area when the worker enters the area without removing a key.

This safety verification system for a extensive area comprises, the extensive area (hereinafter called 'a safety ensuring area 1') where plural workers enter and leaves, one or two and more machines 2 installed in the safety ensuring area, a fixing guard 3 provided around the safety ensuring area, an opening portion 4 provided on a part of the fixing guard so as to allow workers to enter/leave the safety ensuring area, a monitoring device 5 installed in the opening portion for observing the workers to enter/leave the safety ensuring area, key boxes 6, 7 provided on the outside and inside of the safety ensuring area and corresponding to the number of the workers, keys 8 capable of being inserted in the key boxes and corresponding to the number of the workers, a reset device 9 provided on the outside of the safety ensuring area, a control device 10 giving the machine an operation instruction as an input with information from the monitoring device and the key boxes.