An airway adaptor includes a tubular member to which a measuring section configured to measure a flow rate of a respiratory gas of a subject is to be attached. The tubular member includes: a gas passage through which the respiratory gas to pass； and a resistance portion which is configured to generate a differential pressure in the respiratory gas passing through the gas passage, the resistance portion includes at least two partition members which are disposed in the gas passage along an axial direction of the tubular member and which are separated from one another, and side surfaces of the partition members are separated from an inner wall surface of the gas passage.
