A heat exchanger comprising a header (70, 270) and a plurality of heat transfer tubes connected to the header, wherein the header has a plurality of members including a first member (71, 271, 275), a second member (72, 273), and a third member (73, 272, 274) which are brazed, wherein the first member has a first portion, the first portion having a plate shape and a plurality of first openings into which the heat transfer tubes are inserted, the third member is a plate-shaped member having a plurality of second openings into which the heat transfer tubes are inserted, the first portion and the third member are laminated in a thickness direction, in a view along an extending direction of the heat transfer tubes, each of the first openings has an outline positioned inside an outline of a corresponding one of the second openings, and characterised in that a brazing layer (C3, C7, C9) between the second member and the third member has a melt rate, at a predetermined temperature, being larger than a melt rate, at the predetermined temperature, of at least one of a brazing layer (C2, C6, C8) between the first member and the second member and a brazing layer between the first member and the third member, wherein the brazing layer between the second member and the third member is disposed inside a space defined by the brazing layer between the first member and the second member and the brazing layer between the first member and the third member, and in that the brazing layer (C3, C7, C9) between the second member and the third member has a silicon content larger than a silicon content of at least one of a brazing layer (C2, C6, C8) between the first member and the second member and a brazing layer between the first member and the third member. the header has a plurality of members including a first member (71, 271, 275), a second member (72, 273), and a third member (73, 272, 274) which are brazed, wherein the first member has a first portion, the first portion having a plate shape and a plurality of first openings into which the heat transfer tubes are inserted, the third member is a plate-shaped member having a plurality of second openings into which the heat transfer tubes are inserted, the first portion and the third member are laminated in a thickness direction, in a view along an extending direction of the heat transfer tubes, each of the first openings has an outline positioned inside an outline of a corresponding one of the second openings, and characterised in that a brazing layer (C3, C7, C9) between the second member and the third member has a melt rate, at a predetermined temperature, being larger than a melt rate, at the predetermined temperature, of at least one of a brazing layer (C2, C6, C8) between the first member and the second member and a brazing layer between the first member and the third member, wherein the brazing layer between the second member and the third member is disposed inside a space defined by the brazing layer between the first member and the second member and the brazing layer between the first member and the third member, and in that the brazing layer (C3, C7, C9) between the second member and the third member has a silicon content larger than a silicon content of at least one of a brazing layer (C2, C6, C8) between the first member and the second member and a brazing layer between the first member and the third member.