To improve the heat exchanging ability of a heat exchanger as a whole by increasing all heat transfer areas of fins in a limited space in the heat exchanger.

The heat exchanger comprises a casing, a partition wall by which the casing is divided into two heat exchanging chambers, at least one heat pipe passing through the partition wall to protrude to both the heat exchanging chambers and having a tapered end and many fins provided in parallel at prescribed intervals in the longitudinal direction in the part except the end of the heat pipe. The heat pipe has a small diameter and is further provided with a least one fin in the part except the end thereof. Thus, when the heat pipe having a prescribed length has the small diameter, the end of the heat pipe is short. Conversely, the part except the end is long. Accordingly, the part except the end whose length is increased is further provided with the number of fins corresponding to the length of the part whose length is increased.