Shift lenses 20L, 20R are provided on optical axes that pass through LCDs 40L, 40R for displaying an image for focusing. The shift lenses 20L, 20R are moved along the optical axes by pressing a focus button provided on a case 10 in accordance with an instruction displayed on the LCDs 40L, 40R. An amplitude of accommodation is calculated on the basis of a position where the image starts blurring upon moving the shift lenses 20L, 20R from a far point side focus position, and a position where the image starts blurring upon moving the shift lenses 20L, 20R from a near point side focus position.
