An indoor unit (500, 700) for an air-conditioning apparatus, the indoor unit (500, 700) comprising: a casing having an air inlet and an air outlet and being configured to be installed in a room to be air-conditioned; an air-sending fan configured to generate an air flow from the air inlet to the air outlet; a heat exchanger forming a part of a refrigerant circuit filled with refrigerant and configured to allow the air flow generated by the air-sending fan to pass through the heat exchanger; a heat exchanger chamber formed in the casing, configured to accommodate the air-sending fan and the heat exchanger, and communicate with the air inlet and the air outlet; a communication pipe forming a part of the refrigerant circuit and connected to the heat exchanger; an external connection pipe forming a part of the refrigerant circuit and introduced into the room from an outside of the room; a pipe chamber formed separately from the heat exchanger chamber in the casing and accommodating a connection portion of the communication pipe and the external connection pipe; a first refrigerant sensor provided in a lower portion of the heat exchanger chamber and configured to detect the refrigerant; a refrigerant leakage detection sensor (24, 27) provided in the pipe chamber; and a controller configured to control operation of the indoor unit (500, 700), wherein the controller is configured to, when determining that a leakage of the refrigerant is occurring based on a result of detection by the refrigerant leakage detection sensor (24, 27), rotate the air-sending fan, and then stop rotation of the air-sending fan or reduce a rotation speed of the air-sending fan in accordance with a result of detection by the first refrigerant sensor. a casing having an air inlet and an air outlet and being configured to be installed in a room to be air-conditioned; an air-sending fan configured to generate an air flow from the air inlet to the air outlet; a heat exchanger forming a part of a refrigerant circuit filled with refrigerant and configured to allow the air flow generated by the air-sending fan to pass through the heat exchanger; a heat exchanger chamber formed in the casing, configured to accommodate the air-sending fan and the heat exchanger, and communicate with the air inlet and the air outlet; a communication pipe forming a part of the refrigerant circuit and connected to the heat exchanger; an external connection pipe forming a part of the refrigerant circuit and introduced into the room from an outside of the room; a pipe chamber formed separately from the heat exchanger chamber in the casing and accommodating a connection portion of the communication pipe and the external connection pipe; a first refrigerant sensor provided in a lower portion of the heat exchanger chamber and configured to detect the refrigerant; a refrigerant leakage detection sensor (24, 27) provided in the pipe chamber; and a controller configured to control operation of the indoor unit (500, 700), wherein the controller is configured to, when determining that a leakage of the refrigerant is occurring based on a result of detection by the refrigerant leakage detection sensor (24, 27), rotate the air-sending fan, and then stop rotation of the air-sending fan or reduce a rotation speed of the air-sending fan in accordance with a result of detection by the first refrigerant sensor.