A semifinished joint plate 60 has a refrigerant inlet portion 45 and a refrigerant outlet portion 46 spaced apart in the front-rear direction. The semifinished plate 60 has an upwardly or downwardly extending slit 61 formed between the inlet portion 45 and the outlet portion 46, and slit width adjusting portions 62, 63 extending through the thickness of the plate 60, having a larger width than the slit 61 and communicating respectively with the upper and lower ends of the slit 61. A portion of the semifinished plate 60 above the upper adjusting portion 62 and a portion thereof below the lower adjusting portion 63 are bent to shorten the plate.