The coolant evaporator has four core sections. A portion of the coolant passes through a first core section (1021a) and a fourth core section (1011b). The remainder of the coolant passes through a second core section (1021b) and a third core section (1011a). An interchanging section (1030) interchanges the positions where the coolant flows. The pathway (1033b) that connects the second core section with the third core section goes through a narrowing pathway (1033k) inside a middle tank section (1033). The narrowing pathway and the end of the middle tank section turn the flow of the coolant so as to flow toward a partition member (1013c). Communicating sections (1032a, 1032b), which connect the middle tank section with distributing sections (1013a, 1013b) have long thin openings. Because the distribution of liquid coolant is adjusted by the narrowing pathway, the concentration of liquid coolant in the vicinity of the outlet (1012a) of the third core section is limited. Concentration of liquid coolant at the core sections that are located downstream in the coolant flow is thereby limited.