The ornamental design for a head mounted displaydevice, as shown and described.
FIG. 1 is a perspective view of a head mounted display device showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a reference view thereof showing an example of the usage of the subject design;
FIG. 9 is a reference view thereof showing that the subject design can be adjusted to the head size of the user by extending the length of optical module part and can be swivelling the optical module part; and,
FIG. 10 is a reference view thereof showing the part of the head mounted display device which is consisted of transparent material by hatching.
The broken lines depict portions of the head mounted display device that form no part of the claimed design.