PURPOSE: To decrease the curvature radius of bent parts by setting the height of the swollen parts of parts to be bent higher than that of the swollen parts of flat remaining parts in the roll board panel used as an evaporator of a refrigerator, a showcase or the like.

CONSTITUTION: Since the height h1 of swollen parts 11a of parts 12 to be bent are set higher than the height h2 of flat remaining parts 14, even when the curvature radius of bent parts R is decreased, the swollen parts 11a are hardly crushed, and the increase in the circuit resistance is small. Since such swollen parts 11a are provided in a plurality of rows, even if each swollen part 11a is crushed to a certain degree, the increase in the circuit resistance of all the swollen parts 11a of the bent part R is small. Accordingly, it is possible to set the curvature radius of the bent part to 20mm or less, for example. Thus, the available inner capacity and the available area on respective surfaces can be increased.