A stress distribution resulting from variation in in-plane film quality of a stress relaxation layer and a reflective layer is eliminated. A reflective layer is stacked on a substrate via a stress relaxation layer. The stress relaxation layer has a stress relaxation portion having a uniform film thickness distribution to cancel the internal stress of the reflective layer, and a stress distribution eliminating portion with a film thickness distribution approximated to a second order even function. The stress is substantially proportional to the film thickness. Thus, formation of a given film thickness distribution allows the stress distribution to be controlled. However, changing the film thickness distribution based on a design value may degrade the optical characteristics. Thus, the film thickness distribution of the stress distribution eliminating portion, which serves to eliminate the stress distribution, is approximated to the second order even function. This enables aberration associated with the film thickness distribution to be reduced by adjusting an optical system.