A HMD device including a display, a first waveguide element and a second waveguide element is provided. The first waveguide element comprises a first light incident surface, a first light emerging surface and a plurality of first light splitting elements. An image beam is incident to the first waveguide element through the first light incident surface, and leaves the first waveguide element through the first light emerging surface. The second waveguide element comprises a second light incident surface, a second light emerging surface and a plurality of second light splitting elements. The image beam is incident to the second waveguide element through the second light incident surface. The image beam leaves through the second light emerging surface and is projected to the projection target. A reflectivity of the Nth one of the second light splitting elements is smaller than or equal to a reflectivity of the (N+1)th one of the second light splitting elements.