To provide a cover member for a water spray tank, which prevents cooling water from scattering to the outside even when a flow rate of the cooling water is high.

In this cover member 10 for the water spray tank covering a top portion of the water spray tank 5 comprising a water pipe 6 for supplying the cooling water upward, side plates 10b, 10c, 10d from a peripheral edge of a top plate 10a of the cover member 10 for the water spray tank are vertically disposed in the state where gaps are not found among the side plates 10b, 10c, 10d, to form the cover member 10 for the water spray tank into the box shape opened at its lower portion.