Provided is an evaporator including a header in which a depressed portion is formed by concavely depressing downwards a transverse central portion in a longitudinal direction from an upper surface, the portion in which the depressed portion is formed protrudes downwards to form a pair of partitions spaced apart from each other, and a communication hole is formed in a penetrating manner in a transverse direction in each of the pair of partitions; a tank in which a transverse central portion is coupled to a lower end of the partition of the header and both sides in the transverse direction are coupled to the header; and an insert plate inserted into the depressed portion of the header such that both surfaces are tightly attached to the pair of partitions, and having a through hole provided at a position corresponding to the communication holes provided in the pair of partitions.