To prevent the development of winkle in a metallic strip and the bending of a roll and to improve the thermal efficiency in a heat treatment furnace by improving the heat resistance, wear resistance, resistance to melt- sticking of foreign material, heat-insulating property and durability of a conveying roll in a furnace.

An inner cylinder 14 regulating a plurality of layers of coolant flowing passages 19, 20 in the inner part of the roll body 13 and spiral coolant flowing passage is formed in each coolant flowing passage with linear spacers 18. On the outer peripheral surface of the roll body 13, a thermal-sprayed layer 43 is formed and the coolant temp. at the outlet side of each of the coolant flowing passages 19, 20, is individually controlled so as to become the preset target temp. at the higher temp. as the coolant flowing passage is at more outer side.