A glass substrate-holding tool employed during the production of a reflective mask blank for EUV lithography includes an electrostatic chuck and a mechanical chuck. A caught and held portion of a glass substrate caught and held by the electrostatic chuck, and pressed portions of the glass substrate pressed by the mechanical chuck are located outside a quality-guaranteed region on each of a film deposition surface and a rear surface of the glass substrate. The sum of a catching and holding force applied to the glass substrate by the electrostatic chuck and a holding force applied to the glass substrate by the mechanical chuck is at least 200 kgf. A pressing force per unit area applied to the glass substrate by the mechanical chuck is at most 25 kgf/mm2.