A heat exchanger, in which heat is exchanged between first and second mediums, includes a housing that includes a first inlet and a first outlet, an internal member that divides a space in the housing into first and second chambers, and first and second external channels, through which the first medium flows, in the respective first and second chambers. The internal member includes a diverging hole that divides the first medium into flows through the first and second external channels, a converging hole that allows the divided first medium to converge, a second inlet, a second outlet, and an internal channel through which the second medium flows. The first and second external channels each include a first bent portion bent inwardly at a peripheral portion of the first or second chamber. The internal channel includes a second bent portion bent inwardly at a peripheral portion of the internal member.