The present invention provides a variable slit apparatus, which can rapidly change the shape of the slit width of the illumination light while finely controlling the shape of the slit-shaped illumination light, an illumination apparatus that uses such, an exposure apparatus, and the like. The variable slit apparatus for forming a slit-shaped illumination light comprises: a first light-shielding mechanism that comprises a plurality of blades for defining one long side of the illumination light; a second light-mechanism configured to define another long side of the illumination light; and a drive mechanism that changes the width of the illumination light in the latitudinal direction orthogonal to the longitudinal direction by driving the first light-shielding mechanism and the second light-shielding mechanism.