A method of counting the number of puffs using an aerosol generating device is disclosed. The may include obtaining a first start time which is a time when a pressure measured by a sensor included in the aerosol generating device decreases below a first reference pressure value; obtaining a first end time which is a time when the pressure measured by the sensor reaches the first reference pressure value after the first start time; determining whether a first period, which is a period between the first end time and the first start time, is longer than or equal to a first reference period; and increase the number of puffs by one based on the first period being longer than or equal to the first reference period.