An exposure apparatus including a projection optical system for projecting a pattern of a reticle onto a plate to be exposed, via a liquid that is filled in a space between the projection optical system and the plate, a supply pipe for supplying the liquid to the space between a final surface in the projection optical system and the plate, a recovery pipe for recovering the liquid from the space between the final surface in the projection optical system and the plate, and a measuring apparatus for measuring a refractive index of the liquid. The measuring apparatus includes (i) a cell for accommodating the liquid and transmitting light, wherein the cell is connected to one of the supply pipe and the recovery pipe, and (ii) a detector for detecting an incident position of the light refracted by the liquid in the cell.