To provide a welded plate type heat exchange enabling multipath type.

The welded plate type heat exchange 40 includes a partitioning plate 41, which has a passage hole opened and corresponding only to one to three passage holes out of two first passage holes 15, 16 and two second passage holes 17, 18, interposed in an intermediate part of a plate cassette 12 when the plate cassette 12 is laminated. The welded plate type heat exchange 40 is one of the multipath type capable of exchanging heat of a first fluid and a second fluid respectively on left and right sides of the partitioning plate 41. A plate 14 with four passage holes 15, 16, 17, 18 formed thereon is used for each of the plate cassettes 12. Therefore, it is not necessary to worry about an organization of the plate 14 stacked in producing the plate cassette 12, and manufacturing cost can be reduced and manufacturing operation can be simplified.