An indoor unit of an air-conditioning apparatus, the indoor unit comprising: a suction grille having an air inlet through which air flows in; a decorative panel to which the suction grille is mounted and having an air outlet through which the air flows out; a casing to which the decorative panel is mounted and defining an air passage between the air inlet and the air outlet; a fan located to face the suction grille in the casing and configured to cause the air to flow in through the air inlet and flow out through the air outlet; a heat exchanger located in the air passage between the fan and the air outlet in the casing and configured to exchange heat between refrigerant flowing in the heat exchanger and the air; a refrigerant detection sensor configured to detect leakage of the refrigerant, the suction grille being located below the heat exchanger, the refrigerant detection sensor being located below the heat exchanger and between the suction grille and the fan, characterized in that the indoor unit further comprises: a sensor holder shaped in a box shape and containing the refrigerant detection sensor, the sensor holder being configured to secure the refrigerant detection sensor in the casing; and a temperature sensor located in the sensor holder and configured to detect a temperature of the air flowing in through the air inlet, the sensor holder including a first housing portion housing the refrigerant detection sensor, and a second housing portion housing the temperature sensor, a partition separating a space in the first housing portion from a space in the second housing portion. a suction grille having an air inlet through which air flows in; a decorative panel to which the suction grille is mounted and having an air outlet through which the air flows out; a casing to which the decorative panel is mounted and defining an air passage between the air inlet and the air outlet; a fan located to face the suction grille in the casing and configured to cause the air to flow in through the air inlet and flow out through the air outlet; a heat exchanger located in the air passage between the fan and the air outlet in the casing and configured to exchange heat between refrigerant flowing in the heat exchanger and the air; a refrigerant detection sensor configured to detect leakage of the refrigerant, the suction grille being located below the heat exchanger, the refrigerant detection sensor being located below the heat exchanger and between the suction grille and the fan, characterized in that the indoor unit further comprises: a sensor holder shaped in a box shape and containing the refrigerant detection sensor, the sensor holder being configured to secure the refrigerant detection sensor in the casing; and a temperature sensor located in the sensor holder and configured to detect a temperature of the air flowing in through the air inlet, the sensor holder including a first housing portion housing the refrigerant detection sensor, and a second housing portion housing the temperature sensor, a partition separating a space in the first housing portion from a space in the second housing portion. a sensor holder shaped in a box shape and containing the refrigerant detection sensor, the sensor holder being configured to secure the refrigerant detection sensor in the casing; and a temperature sensor located in the sensor holder and configured to detect a temperature of the air flowing in through the air inlet, the sensor holder including a first housing portion housing the refrigerant detection sensor, and a second housing portion housing the temperature sensor, a partition separating a space in the first housing portion from a space in the second housing portion.