PURPOSE: To enable production of a plate-shaped body having high smoothness of flat surface and having no stain or scratch, etc., by cooling a belt of a plate- shaped body immediately after forming on the upper surface of a holding box provided by combining a projected part water cooling part gas blowing part and a gas sucking part while supporting the plate-shaped body uniformly.

CONSTITUTION: A copper projected part 2 having knife-shaped sectional form plated with Cr on the surface is attached to the tip end integrally facing the upper surface of the main body of a holding box 1 for a plate-shaped body belt. The amt. of water to be passed is adjusted by providing a charging and discharging ports of water by providing several partitioning walls and weirs to the inside of the holding box 1. A water cooling part 4, a gas blowing part 5 and a gas sucking part 6 having both nozzles of specified diameters, are provided to the main body part repeatedly facing the upper side of the main body so as to embrace the water cooling part 4 to construct thus an upper part of a lower gas chamber 3. The charge and discharge of gas and the control of the amt. of the gas are performed in the chamber 3. A plate-shaped body belt 16 rolled by an upper and lower forming roll 13, 14 is cooled while holding the belt with said holding box 1.