A refrigerant passage of an evaporator, in which refrigerant flows, is divided into plural sub-passages by partition wall portions of inner fins. The partition wall portions have plural louvers for flowing the refrigerant from an air flow downstream side sub-passage to an ajdacent air flow upstream side sub-passage. The louvers are alternately arranged on the partition wall portions with specific intervals in a refrigerant flow direction. Accordingly, refrigerant distributed amounts into the plural sub-passages can be adjusted to correspond to variations in thermal load on an air side.