An air-conditioner comprising: an air channel; a fan configured to cause an airflow passing through the air channel; a heat exchanger disposed in the air channel to cause a heat-exchange between refrigerant flowing therein and air passing therethrough; refrigerant pipes (283, 284) for supplying refrigerant to the heat exchanger and discharging the refrigerant from the heat exchanger; a semi-conductor gas sensor disposed in the air channel and reactive to at least predetermined refrigerant to output a detection value indicating a level of intensity of reaction of the semi-conductor gas sensor; a first determination section configured to determine whether or not the detection value is equal to or greater than a first threshold when the fan is in operation, and determine that a refrigerant leakage has occurred on condition that the detection value is determined as being equal to or greater than the first threshold when the fan is in operation; and a detection result utilization section configured to take a predetermined action for outputting alarm information and/or limiting supply of refrigerant to the heat exchanger when a refrigerant leakage is determined to have occurred by the first determination section, characterized by a second determination section configured to determine whether or not the detection value is equal to or greater than a second threshold when the fan is not in operation, the second threshold being the same as or different from the first threshold, and, if the detection value is determined as being equal to or greater than the second threshold when the fan is not in operation, start operation of the fan as a provisional operation, stop the provisional operation of the fan, determine whether or not the detection value is equal to or greater than a third threshold after stopping the provisional operation of the fan, and determine that a refrigerant leakage has occurred on condition that the detection value is determined as being equal to or greater than a third threshold after stopping the provisional operation of the fan, the third threshold being the same as or different from each of the first threshold and the second threshold, wherein the detection result utilization section is further configured to take the predetermined action when a refrigerant leakage is determined to have occurred by the second determination section. an air channel; a fan configured to cause an airflow passing through the air channel; a heat exchanger disposed in the air channel to cause a heat-exchange between refrigerant flowing therein and air passing therethrough; refrigerant pipes (283, 284) for supplying refrigerant to the heat exchanger and discharging the refrigerant from the heat exchanger; a semi-conductor gas sensor disposed in the air channel and reactive to at least predetermined refrigerant to output a detection value indicating a level of intensity of reaction of the semi-conductor gas sensor; a first determination section configured to determine whether or not the detection value is equal to or greater than a first threshold when the fan is in operation, and determine that a refrigerant leakage has occurred on condition that the detection value is determined as being equal to or greater than the first threshold when the fan is in operation; and determine whether or not the detection value is equal to or greater than a first threshold when the fan is in operation, and determine that a refrigerant leakage has occurred on condition that the detection value is determined as being equal to or greater than the first threshold when the fan is in operation; and a detection result utilization section configured to take a predetermined action for outputting alarm information and/or limiting supply of refrigerant to the heat exchanger when a refrigerant leakage is determined to have occurred by the first determination section, characterized by a second determination section configured to determine whether or not the detection value is equal to or greater than a second threshold when the fan is not in operation, the second threshold being the same as or different from the first threshold, and, if the detection value is determined as being equal to or greater than the second threshold when the fan is not in operation, start operation of the fan as a provisional operation, stop the provisional operation of the fan, determine whether or not the detection value is equal to or greater than a third threshold after stopping the provisional operation of the fan, and determine that a refrigerant leakage has occurred on condition that the detection value is determined as being equal to or greater than a third threshold after stopping the provisional operation of the fan, the third threshold being the same as or different from each of the first threshold and the second threshold, wherein the detection result utilization section is further configured to take the predetermined action when a refrigerant leakage is determined to have occurred by the second determination section.