A heat exchanger tube which can be integrated with a fin while being stacked on the fin and which can be inserted into a tube insertion hole formed in a header tank to constitute a heat exchanger, the heat exchanger tube comprising: a tube body part which is obtained by bending one sheet of a plate material and which forms a refrigerant flow path having a long, flat cross section in an airflow direction of outside air; and an inner fin which is made of a plate material different from the plate material forming the tube body part and which is arranged in the refrigerant flow path, wherein the tube body part includes: a first flat wall section and a second flat wall section which extend in the airflow direction of outside air and are spaced from each other in a thickness direction of the tube body part; an end-wall section on one side which connects one end section of the first flat wall section in the airflow direction of outside air and one end section of the second flat wall section in the airflow direction of outside air; and an end-wall section on the other side which connects the other end section of the first flat wall section in the airflow direction of outside air and the other end section of the second flat wall section in the airflow direction of outside air, and the plate material forming the tube body part is bent toward the other side at the one end section of the first flat wall section in the airflow direction of outside air and is bent toward the one side at the other end section of the first flat wall section in the airflow direction of outside air, and the plate material forming the tube body part includes: a first middle column section and a second middle column section which protrude from an intermediate section of the second flat wall section in the airflow direction of outside air toward an inner surface of the first flat wall section and are joined to the inner surface of the first flat wall section; the heat exchanger tube being characterized in that the plate material further includes an overlapping section extending from a protruding end of the first middle column section toward an inner surface of the end-wall section on one side and layered on, and joined to, the inner surface of the end-wall section on one side. a tube body part which is obtained by bending one sheet of a plate material and which forms a refrigerant flow path having a long, flat cross section in an airflow direction of outside air; and an inner fin which is made of a plate material different from the plate material forming the tube body part and which is arranged in the refrigerant flow path, wherein the tube body part includes: a first flat wall section and a second flat wall section which extend in the airflow direction of outside air and are spaced from each other in a thickness direction of the tube body part; an end-wall section on one side which connects one end section of the first flat wall section in the airflow direction of outside air and one end section of the second flat wall section in the airflow direction of outside air; and an end-wall section on the other side which connects the other end section of the first flat wall section in the airflow direction of outside air and the other end section of the second flat wall section in the airflow direction of outside air, and the plate material forming the tube body part is bent toward the other side at the one end section of the first flat wall section in the airflow direction of outside air and is bent toward the one side at the other end section of the first flat wall section in the airflow direction of outside air, and the plate material forming the tube body part includes: a first middle column section and a second middle column section which protrude from an intermediate section of the second flat wall section in the airflow direction of outside air toward an inner surface of the first flat wall section and are joined to the inner surface of the first flat wall section; the heat exchanger tube being characterized in that the plate material further includes an overlapping section extending from a protruding end of the first middle column section toward an inner surface of the end-wall section on one side and layered on, and joined to, the inner surface of the end-wall section on one side.