A head-mounted display, comprising: a light source apparatus (32, 52R, 52L); a display element (10R, 10L) for displaying an image from a display image signal generating apparatus or a night vision camera (21R, 21L) and illuminating the displayed image with light emitted from the light source apparatus (32, 52R, 52L) so that image display light for showing the image is emitted; and a visor or a combiner placed in front of a wearer's eyes, wherein the image display light emitted from said display element is guided to the wearer via said visor or combiner so that a virtual image of an object to be observed is formed in front of said wearer, wherein said light source apparatus (32, 52R, 52L) is made up of a first light source for emitting light with high intensity and a second light source (52R, 52L) for emitting light with low intensity, the head-mounted display is provided with a switching unit for switching light between the light emitted from said first light source or the light emitted from said second light source (52R, 52L), said night vision camera (21R, 21L), said display element (10R, 10L), visor or combiner and the second light source (52R, 52L) are attached to a wearable unit worn on the head of the wearer, the display image signal generating apparatus and said first light source are attachable to a vehicle which the wearer gets in and are connected to the wearable unit through an optical transmission path, and an image from the display image signal generating apparatus is displayed by means of the display element (10R, 10L) when the switching unit allows the first light source to emit light, whereas an image from the night vision camera (21R, 21L) is displayed by means of the display element (10R, 10L) when the switching unit allows the second light source (52R, 52L) to emit light. a light source apparatus (32, 52R, 52L); a display element (10R, 10L) for displaying an image from a display image signal generating apparatus or a night vision camera (21R, 21L) and illuminating the displayed image with light emitted from the light source apparatus (32, 52R, 52L) so that image display light for showing the image is emitted; and a visor or a combiner placed in front of a wearer's eyes, wherein the image display light emitted from said display element is guided to the wearer via said visor or combiner so that a virtual image of an object to be observed is formed in front of said wearer, wherein said light source apparatus (32, 52R, 52L) is made up of a first light source for emitting light with high intensity and a second light source (52R, 52L) for emitting light with low intensity, the head-mounted display is provided with a switching unit for switching light between the light emitted from said first light source or the light emitted from said second light source (52R, 52L), said night vision camera (21R, 21L), said display element (10R, 10L), visor or combiner and the second light source (52R, 52L) are attached to a wearable unit worn on the head of the wearer, the display image signal generating apparatus and said first light source are attachable to a vehicle which the wearer gets in and are connected to the wearable unit through an optical transmission path, and an image from the display image signal generating apparatus is displayed by means of the display element (10R, 10L) when the switching unit allows the first light source to emit light, whereas an image from the night vision camera (21R, 21L) is displayed by means of the display element (10R, 10L) when the switching unit allows the second light source (52R, 52L) to emit light.