lid 20 are not disjoined when the brazing material 32 held on the interior surface of each through hole 40 by surface tension is solidified finally it serves as a stopper that blocks off the through holes 40 accordingly there is no possibility that the cooling water flowing through the cooler 10 leaks to the outside through the through holes 40 in example 3 fig9 and 10 show one insulating member 12 indicated by a chain double dashed line in fig2 to show a joining portion between the insulating member 12 and the lid 20 specifically fig9 is a perspective view showing the insulating member 12 and the lid 20 in an exploded state fig1 is a top view showing the insulating member 12 and the lid 20 in a joining state a sectional view taken along a line c c in fig1 is identical to fig6 and omitted herein as shown in fig9 and 10 the lid 20 is provided with the through hole 40 and a sloping portion 46 in this example the details of the through hole 40 are identical to those in example 1 or example 2 and omitted herein the sloping portion 46 is a cone shaped sloping hollow centered at the through hole 40 as shown in fig9 this sloping portion 46 is one example of a passage communicated with the through hole 40 as with the grooves 42 of example 1 and the grooves 44 of example 2 the sloping portion 46 is provided between a position z at a predetermined distance apart from the edge 39 a of the joining portion 39 between.