An air conditioning apparatus, comprising: a duct that is configured to connect the air conditioning apparatus to a plurality of blow-out ports (9a to 9h) formed in an air-conditioning target space (7a, 7b) and that is configured to send air to the blow-out ports (9a to 9h); a casing that includes an inlet port that takes in air and an outlet port to which the duct is connected, the casing forming an airflow path extending from the inlet port to the outlet port; a fan that is disposed in the casing and is configured to send air from the inlet port to the outlet port in the airflow path; an air filter that is disposed in the airflow path and that is configured to purify air, and a heat exchanger that is disposed in the airflow path and that is configured to adjust a temperature of air, the air filter or the heat exchanger being a ventilation member that allows air to pass therethrough; wherein the air conditioning apparatus further includes: a differential pressure gauge that is configured to measure a differential pressure between points in front of and behind the ventilation member; and a controller that is configured to adjust a rotational speed of the fan based on a measured value of the differential pressure gauge characterized in that a first variable-opening damper (6a, 6b) is disposed in the duct and is configured to control the distribution of flow to the plurality of blow-out ports (9a to 9h), and wherein the controller is configured to reduce the rotational speed of the fan to a first correction speed when the measured value of the differential pressure gauge decreases by a first predetermined value or more within a first predetermined time, when the first variable-opening damper is fully closed. a duct that is configured to connect the air conditioning apparatus to a plurality of blow-out ports (9a to 9h) formed in an air-conditioning target space (7a, 7b) and that is configured to send air to the blow-out ports (9a to 9h); a casing that includes an inlet port that takes in air and an outlet port to which the duct is connected, the casing forming an airflow path extending from the inlet port to the outlet port; a fan that is disposed in the casing and is configured to send air from the inlet port to the outlet port in the airflow path; an air filter that is disposed in the airflow path and that is configured to purify air, and a heat exchanger that is disposed in the airflow path and that is configured to adjust a temperature of air, the air filter or the heat exchanger being a ventilation member that allows air to pass therethrough; wherein the air conditioning apparatus further includes: a differential pressure gauge that is configured to measure a differential pressure between points in front of and behind the ventilation member; and a controller that is configured to adjust a rotational speed of the fan based on a measured value of the differential pressure gauge characterized in that a first variable-opening damper (6a, 6b) is disposed in the duct and is configured to control the distribution of flow to the plurality of blow-out ports (9a to 9h), and wherein the controller is configured to reduce the rotational speed of the fan to a first correction speed when the measured value of the differential pressure gauge decreases by a first predetermined value or more within a first predetermined time, when the first variable-opening damper is fully closed. a differential pressure gauge that is configured to measure a differential pressure between points in front of and behind the ventilation member; and a controller that is configured to adjust a rotational speed of the fan based on a measured value of the differential pressure gauge characterized in that a first variable-opening damper (6a, 6b) is disposed in the duct and is configured to control the distribution of flow to the plurality of blow-out ports (9a to 9h), and wherein the controller is configured to reduce the rotational speed of the fan to a first correction speed when the measured value of the differential pressure gauge decreases by a first predetermined value or more within a first predetermined time, when the first variable-opening damper is fully closed.