limit see formula 1 in a case where the plate thickness tf of the fin is 0 06 mm and a straight line c is the machining upper limit see formula 1 in a case where the plate thickness tf of the fin is 0 16 mm a straight line d indicates a lower limit of wh u2212 tf pf at which the fan matching heat radiation amount ratio becomes larger than 100 in consideration of the machining upper limit and is obtained by simultaneously setting up the upper limit of wh wh 0 3674 u00b7 wp 1 893 u00b7 tf u2212 0 1584 in formula 1 and the lower limit 0 088 wh u00b7 tf pf of wh u2212 tf pf in formula 2 and by deleting tf likewise a straight line e indicates an upper limit of wh u2212 tf pf at which the fan matching heat radiation amount ratio becomes larger than 100 in consideration of the machining upper limit and is obtained by simultaneously setting up the upper limit of wh in formula 1 and the upper limit of 0 342 wh u2212 tf pf of wh u2212 tf pf in formula 2 and by deleting tf that is in the case where the plate thickness tf of the fin is 0 06 mm machining of the fin is possible and the fan matching heat radiation amount ratio thereof becomes larger than 100 in comparison with the conventional type corrugated fin within a.