Provided are a wearable display device and a light guide element thereof, the display device including: 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. The light guide element includes: a first optical surface facing the display element; a second optical surface and a third optical surface configured to reflect the first light input through the first optical surface; and a fourth optical surface configured to reflect the reflected first light to the predetermined position. The first to third optical surfaces are flat surfaces, and the fourth optical surface is a rotationally asymmetric reflective surface.