A heat exchanger comprising: a hollow housing including a first inlet member through which a first medium flows into the housing and a first outlet member through which the first medium flows out of the housing; an internal member disposed in the housing such that a space in the housing is divided into a first chamber and a second chamber; and a first external channel in the first chamber and a second external channel in the second chamber, the first external channel and the second external channel being in communication with the first inlet member and the first outlet member, respectively, such that the first medium flows through the first external channel and the second external channel, characterized by the internal member including: a diverging hole that divides the first medium flowing from the first inlet member into a flow flowing through the first external channel and a flow flowing through the second external channel; a converging hole that allows the divided first medium to converge; a second inlet member through which a second medium flows into the housing; a second outlet member through which the second medium flows out of the housing; and an internal channel that is in communication with the second inlet member and the second outlet member such that the second medium flows through the internal channel, wherein the first external channel and the second external channel each include a first bent portion at which the first external channel and the second external channel are bent inwardly at a peripheral portion of each of the first chamber and the second chamber, and the internal channel includes a second bent portion at which the internal channel is bent inwardly at a peripheral portion of the internal member, and heat is exchanged between the first medium, which flows through the first external channel and the second external channel, and the second medium, which flows through the internal channel. a hollow housing including a first inlet member through which a first medium flows into the housing and a first outlet member through which the first medium flows out of the housing; an internal member disposed in the housing such that a space in the housing is divided into a first chamber and a second chamber; and a first external channel in the first chamber and a second external channel in the second chamber, the first external channel and the second external channel being in communication with the first inlet member and the first outlet member, respectively, such that the first medium flows through the first external channel and the second external channel, the internal member including: a diverging hole that divides the first medium flowing from the first inlet member into a flow flowing through the first external channel and a flow flowing through the second external channel; a converging hole that allows the divided first medium to converge; a second inlet member through which a second medium flows into the housing; a second outlet member through which the second medium flows out of the housing; and an internal channel that is in communication with the second inlet member and the second outlet member such that the second medium flows through the internal channel, wherein a diverging hole that divides the first medium flowing from the first inlet member into a flow flowing through the first external channel and a flow flowing through the second external channel; a converging hole that allows the divided first medium to converge; a second inlet member through which a second medium flows into the housing; a second outlet member through which the second medium flows out of the housing; and an internal channel that is in communication with the second inlet member and the second outlet member such that the second medium flows through the internal channel, wherein the first external channel and the second external channel each include a first bent portion at which the first external channel and the second external channel are bent inwardly at a peripheral portion of each of the first chamber and the second chamber, and the internal channel includes a second bent portion at which the internal channel is bent inwardly at a peripheral portion of the internal member, and heat is exchanged between the first medium, which flows through the first external channel and the second external channel, and the second medium, which flows through the internal channel.