Head-mounted display device

A head-mounted display device, comprising:

• a display element;
• a casing accommodating the display element;
• an eyepiece optical system with a positive refractive power, which receives image light incident from the display element, guides the image light to the front of an eyeball of the wearer, and emits the image light toward the eyeball, so as to make observable a virtual image formed by the image light;
• and
• a slide operation portion which is provided so as to be slidable, with respect to the casing, in the anteroposterior direction of the head of the wearer,
• wherein the slide operation portion is coupled to at least either the display element or an optical element in the eyepiece optical system in such a manner that a length of an optical path between the display element and the optical element is increased when the slide operation portion is slid in the anterior direction of the wearer.