A heat exchanger according to the present invention comprises a heat exchange portion in which heating medium flow paths, where a heating medium flows through a space between a plurality of plates, and combustion gas flow paths through which a combustion gas combusted in a burner flows are adjacently and alternatingly formed, wherein the heat exchange portion comprises a sensible heat portion, which surrounds the outside of a combustion chamber and comprises an area on one side of the plates, for heating the heating medium using the sensible heat of the combustion gas generated by combustion of the burner, and a latent heat portion, which comprises an area on the other side of the plates, for heating the heating medium using the latent heat of water vapors in the combustion gas which has completed heat exchanging in the sensible heat portion, wherein a connection passage for the heating medium is formed between the sensible heat portion and the latent heat portion, the plates are formed in a vertical structure so that the sensible heat portion is positioned on the top part and the latent heat portion is positioned on the bottom part, and wherein the burner has a cylindrical shape and is assembled by being inserted laterally from the front surface of a space in the combustion chamber.