A wearable display device comprising: a display element configured to project a first light forming a virtual image; and a light guide element configured to guide the first light from the display element and a second light input from outside of the wearable display device to a predetermined position, wherein the light guide element comprises: a first optical surface through which the first light from the display element is input; a second optical surface configured to reflect the first light input through the first optical surface; a third optical surface configured to reflect the first light which is reflected by the second optical surface; and a fourth optical surface configured to reflect the reflected first light, reflected by the second optical surface and the third optical surface, to the predetermined position, wherein the first optical surface, the second optical surface, and the third optical surface are flat surfaces, and wherein the fourth optical surface is a rotationally asymmetric reflective surface, characterized in that: a distance between an apex of the fourth optical surface and the third optical surface is less than one half of a distance between the second optical surface and the third optical surface, the apex of the fourth optical surface is positioned inside the light guide element, and the apex of the fourth optical surface is the point of highest sag of the fourth optical surface away from a plane which is substantially parallel with the fourth optical surface. a display element configured to project a first light forming a virtual image; and a light guide element configured to guide the first light from the display element and a second light input from outside of the wearable display device to a predetermined position, wherein the light guide element comprises: a first optical surface through which the first light from the display element is input; a second optical surface configured to reflect the first light input through the first optical surface; a third optical surface configured to reflect the first light which is reflected by the second optical surface; and a fourth optical surface configured to reflect the reflected first light, reflected by the second optical surface and the third optical surface, to the predetermined position, wherein the first optical surface, the second optical surface, and the third optical surface are flat surfaces, and wherein the fourth optical surface is a rotationally asymmetric reflective surface, characterized in that: a distance between an apex of the fourth optical surface and the third optical surface is less than one half of a distance between the second optical surface and the third optical surface, the apex of the fourth optical surface is positioned inside the light guide element, and the apex of the fourth optical surface is the point of highest sag of the fourth optical surface away from a plane which is substantially parallel with the fourth optical surface. a first optical surface through which the first light from the display element is input; a second optical surface configured to reflect the first light input through the first optical surface; a third optical surface configured to reflect the first light which is reflected by the second optical surface; and a fourth optical surface configured to reflect the reflected first light, reflected by the second optical surface and the third optical surface, to the predetermined position, wherein the first optical surface, the second optical surface, and the third optical surface are flat surfaces, and wherein the fourth optical surface is a rotationally asymmetric reflective surface, characterized in that: a distance between an apex of the fourth optical surface and the third optical surface is less than one half of a distance between the second optical surface and the third optical surface, the apex of the fourth optical surface is positioned inside the light guide element, and the apex of the fourth optical surface is the point of highest sag of the fourth optical surface away from a plane which is substantially parallel with the fourth optical surface.