An adaptor is adapted to be attached on a face of the subject to collect expiration gas of the subject. An airway case is formed with a chamber, and adapted to be coupled with a carbon dioxide sensor so that carbon dioxide in the expiration gas flowing through the chamber is detected by the carbon dioxide sensor. Nasal tubes are adapted to be inserted into nostrils of the subject when the adaptor is attached on the face of the subject. The nasal tubes are adapted to lead nasal expiration gas of the subject to the chamber. A mouth guide is adapted to lead oral expiration gas of the subject to the chamber when the adaptor is attached on the face of the subject. A branch tube is communicating with the nasal tubes and adapted to lead pressure generated by the nasal expiration gas to an external pressure sensor.
