To provide a jet water apparatus and method of adjusting the height of a jet water nozzle by which jet-stream water from a jet water nozzle is held at proper position of a slab even when there is camber on the slab in the flame scarfing work of the slab.

This jet water apparatus for slab scarfing equipment has an elevating and lowering means of the jet water nozzle which is composed of a sensor 16 for detecting the conveying position of a slab, a device 17 for measuring the amount of conveyance of the slab, a detector 13 of the shape of the slab, an arithmetic unit 18 of the shape of the slab, a roller 6 for positioning the height of the jet water nozzle, a sensor 9 for detecting the height of the jet water nozzle, a screw jack 7 for adjusting the height of the jet water nozzle and an air motor 8 for driving the screw jack and this method of adjusting the height of the water jet nozzle is performed by using the above apparatus.