A heat exchanger comprising: a plurality of tubes in which a heat exchanging medium flows; tank members to which both end portions of these tubes are connected; and a female screw portion, into which a nut for attaching another member to the tank member is incorporated, brazed to the tank member, the female screw portion including: a main body portion, at the center of which a female screw hole is formed, penetrating a wall portion of the tank member; a flange portion, which is formed on one end side in the axial direction of the main body portion, contact with an outer plane of the wall portion; and a groove portion formed on a contact face of the flange portion contact with the outer plane of the wall portion, wherein the flange portion is brazed to the wall portion.