A head-mounted display apparatus including a main body, a mask, and a projection apparatus is provided. The mask is pivotally connected to the main body. The mask includes a reflection area. The reflection area has a first normal line. The projection apparatus is disposed inside the main body and adapted to project an image beam to a target. The projection apparatus includes a mirror. The mirror has a second normal line. An acute angle exists between normal projections of the first normal line and the second normal line on a reference plane.