The present invention provides an exposure apparatus exposing a substrate through a projection optical system, the apparatus comprising a stage configured to hold the substrate, a detection unit configured to emit detection light in a first direction and detect a position of the stage, a blowing unit configured to blow out a gas, and a guide unit including a first portion and a second portion, wherein the first portion is configured to guide the gas to a first space between the projection optical system and the substrate, such that a gas flow along the substrate is formed in the first space, and wherein the second portion is configured to guide the gas to a second space where the detection light passes through, such that a gas flow in a second direction is formed in the second space.