To provide a reticle protection case which is durable in a usage condition of one atmospheric pressure in pressure difference even if the protection case is made thin in wall thickness, and to provide an aligner using the same.

The reticle protection case protects a pattern surface of a reticle 2 from dust and has a mounting mechanism for mounting the case on the reticle removably with leaving a hollow space inside when the case is mounted on the reticle. The case comprises a cover 22a for covering the pattern surface of the reticle 2, a holder 22b for holding the cover, vent holes 31-35 formed on the wall of at least either the cover or holder, communicating with the hollow space, and filters 41-45 mounted to the vent holes for shutting off dust of a specified size or larger from passing.