A head mounted display device, comprising: a housing providing a darkroom space; a display module in the housing, the display module being configured to display an image; and an optical lens being configured to expand the image to provide the image to eyeballs of a user, wherein the display module includes: a first electrode on a base layer; a second electrode closer to the optical lens than the first electrode; a light-emitting element layer including a light-emitting layer between the first and second electrodes (AE, CE); a reflection preventing layer on the second electrode; a phase control layer between the second electrode and the reflection preventing layer, the phase control layer adjusting an optical distance between the second electrode and the reflection preventing layer such that a phase difference between a first light beam, which has been reflected by the optical lens and then by the second electrode, and a second light beam, which has been reflected by the optical lens and then by the reflection preventing layer is 160° to 200° to cause destructive interference; an encapsulating substrate spaced apart from the reflection preventing layer, the encapsulating substrate being configured to encapsulate the light-emitting element layer; and characterized in that the head mounted display device further comprises a phase compensating layer on the phase control layer, wherein the phase compensating layer compensates a phase of the first light beam and a phase of the second light beam so that the phase difference between the first light beam and the second light beam is close to 180°, and a refractive index of the phase compensating layer is less than that of the reflection preventing layer and is greater than that of a medium between the phase compensating layer and the encapsulating substrate. a housing providing a darkroom space; a display module in the housing, the display module being configured to display an image; and an optical lens being configured to expand the image to provide the image to eyeballs of a user, wherein the display module includes: a first electrode on a base layer; a second electrode closer to the optical lens than the first electrode; a light-emitting element layer including a light-emitting layer between the first and second electrodes (AE, CE); a reflection preventing layer on the second electrode; a phase control layer between the second electrode and the reflection preventing layer, the phase control layer adjusting an optical distance between the second electrode and the reflection preventing layer such that a phase difference between a first light beam, which has been reflected by the optical lens and then by the second electrode, and a second light beam, which has been reflected by the optical lens and then by the reflection preventing layer is 160° to 200° to cause destructive interference; an encapsulating substrate spaced apart from the reflection preventing layer, the encapsulating substrate being configured to encapsulate the light-emitting element layer; and characterized in that the head mounted display device further comprises a phase compensating layer on the phase control layer, wherein the phase compensating layer compensates a phase of the first light beam and a phase of the second light beam so that the phase difference between the first light beam and the second light beam is close to 180°, and an encapsulating substrate spaced apart from the reflection preventing layer, the encapsulating substrate being configured to encapsulate the light-emitting element layer; and characterized in that the head mounted display device further comprises a phase compensating layer on the phase control layer, wherein the phase compensating layer compensates a phase of the first light beam and a phase of the second light beam so that the phase difference between the first light beam and the second light beam is close to 180°, and a refractive index of the phase compensating layer is less than that of the reflection preventing layer and is greater than that of a medium between the phase compensating layer and the encapsulating substrate.