A head mounted display comprising: a frame shaped like glasses to be worn on the head of an observer; and an image display apparatus comprising: an image forming device (111, 211); an optical system (112, 254) that converts light emitted from the image forming device (111, 211) into parallel light; and an optical device (120, 320) to which the light beams converted into the parallel light by the optical system (112, 254) enter, in which the light beams are guided, and from which the light beams are emitted, wherein the optical device (120, 320) comprises a light guide plate (121, 321) from which incident light is emitted after the light propagates in the light guide plate (121, 321) by total reflection; when a point where a central light beam that is emitted from the center of the image forming device (111, 211) and passes through the nodal point of the optical system (112, 254) on the side of the image forming device (111, 211) enters the optical device (120, 320) is defined as an optical device center point, an axis that passes through the optical device center point and extends parallel to a virtual straight line connecting the centers of two eyeballs of the observer when the frame is worn on the head of the observer, is defined as an X-axis, and an axis that passes through the optical device center point, and coincides with the normal axis of the optical device (120, 320) at the optical device center point is defined as a Y-axis; the central light beam intersects the XY plane at angles other than 0 degree; and the light guide plate (121, 321) has a first surface (122, 322) and a second surface (123, 323) facing each other, wherein parallel light enters from the first surface (122, 322) serving as a light incident surface, propagates in the light guide plate by total reflection, and is then emitted from the first surface (122, 322) serving as a light exit surface. a frame shaped like glasses to be worn on the head of an observer; and an image display apparatus comprising: an image forming device (111, 211); an optical system (112, 254) that converts light emitted from the image forming device (111, 211) into parallel light; and an optical device (120, 320) to which the light beams converted into the parallel light by the optical system (112, 254) enter, in which the light beams are guided, and from which the light beams are emitted, wherein an image forming device (111, 211); an optical system (112, 254) that converts light emitted from the image forming device (111, 211) into parallel light; and an optical device (120, 320) to which the light beams converted into the parallel light by the optical system (112, 254) enter, in which the light beams are guided, and from which the light beams are emitted, wherein the optical device (120, 320) comprises a light guide plate (121, 321) from which incident light is emitted after the light propagates in the light guide plate (121, 321) by total reflection; when a point where a central light beam that is emitted from the center of the image forming device (111, 211) and passes through the nodal point of the optical system (112, 254) on the side of the image forming device (111, 211) enters the optical device (120, 320) is defined as an optical device center point, an axis that passes through the optical device center point and extends parallel to a virtual straight line connecting the centers of two eyeballs of the observer when the frame is worn on the head of the observer, is defined as an X-axis, and an axis that passes through the optical device center point, and coincides with the normal axis of the optical device (120, 320) at the optical device center point is defined as a Y-axis; the central light beam intersects the XY plane at angles other than 0 degree; and the light guide plate (121, 321) has a first surface (122, 322) and a second surface (123, 323) facing each other, wherein parallel light enters from the first surface (122, 322) serving as a light incident surface, propagates in the light guide plate by total reflection, and is then emitted from the first surface (122, 322) serving as a light exit surface.