smaller than that on the upstream side relatively much cooling medium is distributed to the cooling medium flow portion 11 positioned upstream of the cooling medium flow portion 11 where a cooling medium was apt to remain as the result uniform heat exchange can be carried out in every one of the plurality of cooling flow portions and the heat exchangeability of the heat exchanger is enhanced the sixth example of a heat exchanger according to the present invention will be described with reference to fig2 to 24 a 24 b a cooling medium flow portion is formed by laminating substantially rectangular flat plates 13 and 14 to braze them the actual production of the heat exchanger is not performed by laminating a plurality of brazed cooling medium flow portions and again brazing them to join them but by arranging brazing material clad flat plates 13 and 14 and a cooling fin 12 in this order to laminate them assembling them and other parts and placing the assembly in a heating oven not shown to heat and braze the respective portions in this case the important point is registering the flat plates 13 and 14 however in the heat exchanger of the present example a plurality of spaced positions of outer peripheral portions to be brazed in flat plates 13 and 14 are provided with register positioning portions 23 as shown in fig2 and 23 the register portion 23 is composed of a protrusion portion 24 formed in the flat plate 14 and a concave portion 25 formed in the.