A head-mounted display (HMD) includes a frame configured to be fixated to a head, a light-transmissive display unit fixated to the frame and outputting a VR image in a VR mode and an AR image in an AR mode, a light transmission control layer having changed transmittance, a lens unit having a refractive index changed in the VR mode and the AR mode, and a controller control the light transmission control layer to increase transmittance in the AR mode and decrease transmittance in the VR mode.