Abstract: A cooling apparatus of thick-gauge steel plate having a plurality of pairs of constraining rolls, each comprising a top roll and bottom roll, constraining and conveying hot rolled thick-gauge steel plate and a plurality of spray nozzles spraying water on the top and bottom surfaces of the thick-gauge steel plate conveyed between the adjoining pairs of constraining rolls before and after each other in the conveyance direction, said cooling apparatus of thick-gauge steel plate characterized by arranging said plurality of spray nozzles so that: (i) the sum of the areas of the impact surfaces of the water sprays from the top surface side spray nozzles on the surface of the thick-gauge steel plate is in the range of 4 to 90% of the surface area of the steel plate between the roll outer circumferences at the closest distance between the pairs of constraining rolls and (ii) the sum of the areas of the impact surfaces of the water sprays from the bottom surface side spray nozzles on the surface of the thick-gauge ste