PURPOSE: To prevent clogging due to frosting and to obtain stable heat exchanging performance for a long period by arranging fins alternately deviated laterally at a predetermined interval in a heat exchanger in which a heat medium tube is inserted into the many fins aligned in parallel at a predetermined interval.

CONSTITUTION: This heat exchanger 1 comprises many fins 2 aligned in parallel at a predetermined interval and in which a gas stream flows therebetween, and many heat medium tubes 3 inserted into the fins 2 in such a manner that the fins 2 are arranged alternately laterally at a predetermined interval in a zigzag state. Thus, the fins 2 are arranged in a zigzag state to form a bypass passage 4, thereby preventing clogging due to frosting. Since heat exchanging is executed in the passage 4 through the fins 2 and a gas stream A is dehumidified and cooled, stable heat exchanging performance can be maintained for a long period.