An indoor unit for an air-conditioning apparatus, comprising: a casing , which is to be attached to a wall (K) in a room on a back surface side of the casing ; an air inlet and an air outlet , which are formed in the casing ; an indoor heat exchanger and an indoor fan, which are arranged in an air passage continuous from the air inlet to the air outlet ; an up-and-down airflow direction plate , which is provided in the air outlet so as to be turnable, and forms an air outlet passage for blowing air to be blown out through the air outlet in a region located below the air outlet , and which is configured to change a direction of the blowing air between upward and downward directions; and an up-and-down airflow direction assist plate , which is turned closer to a front surface side of the casing than the up-and-down airflow direction plate , thereby forming the air outlet passage at a position located below the air outlet , and is configured to change the direction of the blowing air in the up-and-down direction, wherein the up-and-down airflow direction assist plate comprises a plate-like portion and an arm portion wherein a rotation locus of a distal end of the up-and-down airflow direction plate crosses a locus of the up-and-down airflow direction assist plate , wherein the distal end of the up-and-down airflow direction plate includes a ridge line portion having a curved surface having a radial dimension R, characterized in that the up-and-down airflow direction assist plate includes a protruding portion protruding by a protruding dimension P on a surface with which the distal end of the up-and-down airflow direction plate is allowed to be in contact, and the protruding dimension P of the protruding portion is smaller than the radial dimension R, and the protruding portion protrudes from a back surface portion of the arm portion . a casing , which is to be attached to a wall (K) in a room on a back surface side of the casing ; an air inlet and an air outlet , which are formed in the casing ; an indoor heat exchanger and an indoor fan, which are arranged in an air passage continuous from the air inlet to the air outlet ; an up-and-down airflow direction plate , which is provided in the air outlet so as to be turnable, and forms an air outlet passage for blowing air to be blown out through the air outlet in a region located below the air outlet , and which is configured to change a direction of the blowing air between upward and downward directions; and an up-and-down airflow direction assist plate , which is turned closer to a front surface side of the casing than the up-and-down airflow direction plate , thereby forming the air outlet passage at a position located below the air outlet , and is configured to change the direction of the blowing air in the up-and-down direction, wherein the up-and-down airflow direction assist plate comprises a plate-like portion and an arm portion wherein a rotation locus of a distal end of the up-and-down airflow direction plate crosses a locus of the up-and-down airflow direction assist plate , wherein the distal end of the up-and-down airflow direction plate includes a ridge line portion having a curved surface having a radial dimension R, characterized in that the up-and-down airflow direction assist plate includes a protruding portion protruding by a protruding dimension P on a surface with which the distal end of the up-and-down airflow direction plate is allowed to be in contact, and the protruding dimension P of the protruding portion is smaller than the radial dimension R, and the protruding portion protrudes from a back surface portion of the arm portion . <EOS>