Exposing apparatus and method for manufacturing article

An exposing apparatus for exposing a substrate comprising:

• a projecting optical system configured to project exposure light to a substrate surface of the substrate;
• a measuring unit configured to measure a position of the substrate in a first direction perpendicular to the substrate surface which is exposed, by making measurement light obliquely incident on the substrate surface and receiving the measurement light reflected by the substrate surface;
• and
• a first gas supplying mechanism including a first gas supplying port for supplying first gas toward a space between the projecting optical system and the measurement light,
• wherein in a second cross section including the first direction and an optical path of the measurement light, a length in a direction orthogonal to the first direction of the first gas supplying port is longer than a length in the direction orthogonal to the first direction of an effective irradiated region of an optical element arranged closest to the substrate among a plurality of optical elements included in the projecting optical system.