A refrigerant evaporator has an interchange part. The interchange part connects a first collecting part of a second downstream tank part, and a second distribution part of a second upstream tank part. The interchange part connects a second collecting part of a second downstream tank part, and a first distribution part of a second upstream tank part. The interchange part swaps a refrigerant about a width direction of a core. Refrigerant passages relevant to the interchange part are configured to improve refrigerant distribution. Providing a plurality of passages and/or twisting a passage improve distribution.