An indoor unit for an air-conditioning apparatus, the indoor unit 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 (G) 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 provided in the pipe chamber ; and a controller configured to control operation of the indoor unit , 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 , 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 (G) 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 provided in the pipe chamber ; and a controller configured to control operation of the indoor unit , 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 , 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 . <EOS>