A viewer includes a multifocal lens capable of setting one of a plurality of focal lengths. When a measuring section detects a change in gazing point distance, a selection section selects a focal length to be set among the plurality of focal lengths, and a determiner determines a time duration before a focal length of the multifocal lens is changed. A controller changes the focal length of the multifocal lens when a detector detects a blink or saccadic eye movement of the user before the determined time duration elapses.