An airway adaptor comprising: a nasal expiration collecting portion which is to be connected to a nostril of a living body, and which is configured to collect an expiration of a nasal cavity; a gas passage portion that forms a gas passage through which the expiration collected by the nasal expiration collecting portion passes; and a gas sensor attaching portion configured to attach a gas sensor in the gas passage portion, wherein the nasal expiration collecting portion is configured to produce a flowing state where a flow of the expiration is allowed, and an obstruction state where the flow of the expiration is blocked, wherein the nasal expiration collecting portion is formed by a flexible member, and includes an obstruction state producing portion which causes the nasal expiration collecting portion to be obstructable, wherein the nasal expiration collecting portion is configured to be bent to obstruct the nasal expiration collecting portion, wherein the obstruction state producing portion includes: a locked portion (113, 114) which is disposed in the nasal expiration collecting portion; and a locking portion (127, 128) which is to be engaged with the locked portion to maintain a state where the nasal expiration collecting portion is bent; and wherein the locked portion is a hole which is formed in the nasal expiration collecting portion, and the locking portion is a projection which is formed on the nasal expiration collecting portion or the gas sensor attaching portion. a nasal expiration collecting portion which is to be connected to a nostril of a living body, and which is configured to collect an expiration of a nasal cavity; a gas passage portion that forms a gas passage through which the expiration collected by the nasal expiration collecting portion passes; and a gas sensor attaching portion configured to attach a gas sensor in the gas passage portion, wherein the nasal expiration collecting portion is configured to produce a flowing state where a flow of the expiration is allowed, and an obstruction state where the flow of the expiration is blocked, wherein the nasal expiration collecting portion is formed by a flexible member, and includes an obstruction state producing portion which causes the nasal expiration collecting portion to be obstructable, wherein the nasal expiration collecting portion is configured to be bent to obstruct the nasal expiration collecting portion, wherein the obstruction state producing portion includes: a locked portion (113, 114) which is disposed in the nasal expiration collecting portion; and a locking portion (127, 128) which is to be engaged with the locked portion to maintain a state where the nasal expiration collecting portion is bent; and a locked portion (113, 114) which is disposed in the nasal expiration collecting portion; and a locking portion (127, 128) which is to be engaged with the locked portion to maintain a state where the nasal expiration collecting portion is bent; and wherein the locked portion is a hole which is formed in the nasal expiration collecting portion, and the locking portion is a projection which is formed on the nasal expiration collecting portion or the gas sensor attaching portion.