To provide a mask (10) capable of reducing a load of a patient while suppressing lowering of accuracy at which an exhaled air of a subject is measured. A mask to be put on a face of a subject includes a mask body portion (20) demarcating an internal space in a state of covering part of the face of the subject and a cup-shaped nasal cup (50) covering a nose (N) of the subject in a state of being arranged inside the internal space, in which the nasal cup includes a first wall portion (51) covering the nose of the subject, a second wall portion (52) arranged under nostrils of the subject, and an exhaled air discharge portion (61) guiding an exhaled air from the nose of the subject to an exhaled air sensor (13), and at least part of the exhaled air from the nose of the subject is guided toward the exhaled air discharge portion by the second guide portion in a state where the nasal cup covers the nose of the subject.
