The invention relates to layered evaporators for use in motor vehicle air conditioners or the like, layered heat exchangers for providing such evaporators, and refrigeration cycle systems comprising the evaporator. At a specified intermediate portion of the heat exchanger with respect to the direction of juxtaposition of intermediate plates, a flat metal plate is interposed between one pair of intermediate metal plates providing a flat tube portion, or between two adjacent flat tube portions. The flat metal plate has a partition portion for blocking the passage of a fluid, a fluid passing hole for permitting passage of the fluid and an uneven flow preventing guide protuberance at an edge portion around the fluid passing hole.The flat plate of very simple structure is used according to the invention as the plate having a partition for providing heat exchanger core passes. This permits use of a simlified plate die of low cost and makes it possible to provide a fluid circuit core having varying pass patterns, and made from a reduced number of components by a simplified assembling procedure which can be automated. The flat plate used further makes it possible to intentionally control the flow of fluid to preclude the occurrence of an uneven flow in the pass and to achieve improved perforamce. The concentration of stress due to the internal pressure of the fluid at the location where the fluid flow is turned is attenuated to give increased pressure resistance to the turn portion and to effectively prevent the break of tank side wall. The heat exchanger is made from metal plates of reduced thickness for a cost reduction and an improvement in heat exchange efficiency.