A head-mounted display device that enables a user to visually recognize a virtual image at the same time as an external scene, comprising: a pair of display drive units (22, 24) that are adapted to generate and emit image light representing an image; and an image processing unit that is adapted to control the display drive units (22, 24) so as to emit the image light from emission areas (CA1, CA2) of the display drive units (22, 24), wherein the image processing unit is adapted to control the pair of display drive units (22, 24) so as to move the emission areas (CA1, CA2) in any one of a first direction in which an image formed by the image light emitted from one of the display drive units and an image formed by the image light emitted from the other of the display drive units move close to each other in cooperation and a second direction in which an image formed by the image light emitted from one of the display drive units and an image formed by the image light emitted from the other of the display drive units move apart from each other in cooperation to change a focal distance (La) of an image in a virtual image which is visually recognized by the user, wherein the emission area (CA1, CA2) is an area smaller in a horizontal direction than a reference area (MA1, MA2) which is an area through which the display drive units (22, 24) are adapted to emit image light in a normal state, the emission area being the area through which image light is actually emitted, characterized in that the head-mounted display device further comprises a marker detecting unit that is adapted to detect a predetermined marker present in front of the user's eyes, and the image processing unit is adapted to change the focal distance (La) of the image when the predetermined marker is detected. a pair of display drive units (22, 24) that are adapted to generate and emit image light representing an image; and an image processing unit that is adapted to control the display drive units (22, 24) so as to emit the image light from emission areas (CA1, CA2) of the display drive units (22, 24), wherein the image processing unit is adapted to control the pair of display drive units (22, 24) so as to move the emission areas (CA1, CA2) in any one of a first direction in which an image formed by the image light emitted from one of the display drive units and an image formed by the image light emitted from the other of the display drive units move close to each other in cooperation and a second direction in which an image formed by the image light emitted from one of the display drive units and an image formed by the image light emitted from the other of the display drive units move apart from each other in cooperation to change a focal distance (La) of an image in a virtual image which is visually recognized by the user, wherein the emission area (CA1, CA2) is an area smaller in a horizontal direction than a reference area (MA1, MA2) which is an area through which the display drive units (22, 24) are adapted to emit image light in a normal state, the emission area being the area through which image light is actually emitted, characterized in that the head-mounted display device further comprises a marker detecting unit that is adapted to detect a predetermined marker present in front of the user's eyes, and the image processing unit is adapted to change the focal distance (La) of the image when the predetermined marker is detected.