PURPOSE: To plan the reduction of thermal stress in the neighborhood of a connecting part by radially arranging a plurality of thermal sleeves with relative intervals on the inner face of a safe end connected to a single tube part on the low temperature side.

CONSTITUTION: A plurality of thermal sleeves 5A, 5B are concentrically arranged on the inner face of a safe end 3 connected to a single water feed tube part 4 and a nozzle 2. Further, a side end part at the side of low temperature of a first cylindrical hollow part 6A between the end 3 and a sleeve 5A and the second cylindrical hollow part 6B, which is moved to the side of low temperature, between the sleeves 5A, 5B are inclined to form. The temperature distribution in the end 3 and the sleeves 5A, 5B is made to function so as to gradually increase in the radially inner direction and the inner direction of a vessel. Therefore, the unevenness of the temperature distribution can be lessened and the production of thermal stress can be reduced.