To provide a sprinkler system of a roof, which decreases a room temperature by cooling a heated roof, which prevents fire spreading in case of a fire of a neighboring house, which removes snow from the roof, which enables installation work to be performed without the modification of a building, and which enables water to be uniformly sprinkled all over the roof without damage to the roof.

In this sprinkler system of the roof, water supply piping is erected from ground in a high position on the extension side of a ridge section of the roof, away from the building; a lower end side of the water supply piping is connected to a water supply source; and a jet nozzle, whose jet orifice has an angle of elevation and which sprinkles the water by emitting a jet of water in the upward direction of the ridge section of the roof, is mounted on the upper end side of the water supply piping.