A head-mounted display apparatus comprising: an image display part configured to display an image; an optical unit (20, 30, 50) configured to lead the image to an eye of a wearer of the display apparatus; a light intensity detector configured to detect light intensity of external light; a dimmer filter configured to vary transmittance to adjust the intensity of the external light reaching the eye of the wearer; and a controller configured to adjust the transmittance of the dimmer filter and the light intensity of a light source of the image display part based on the light intensity of the external light obtained by the light intensity detector; wherein: when the light intensity of the external light is within a first light intensity range, the controller is configured to maintain the light intensity of the light source of the image display part constant, and gradually reduce the transmittance of the dimmer filter as the light intensity of the external light becomes higher; when the light intensity of the external light is within a second light intensity range higher than the first light intensity range, the controller is configured to maintain the transmittance of the dimmer filter constant, and gradually increase the light intensity of the light source of the image display part as the light intensity of the external light becomes higher; and characterised in that: a light intensity ratio is controlled to be comparatively higher if the image is composed of intermediate gradations, and comparatively lower if the image is composed of two gradations, wherein the light intensity ratio is defined as C / B, where C is the light intensity of the image transmitted from the image display part, and B is the intensity of the external light reaching the eye of the wearer. an image display part configured to display an image; an optical unit (20, 30, 50) configured to lead the image to an eye of a wearer of the display apparatus; a light intensity detector configured to detect light intensity of external light; a dimmer filter configured to vary transmittance to adjust the intensity of the external light reaching the eye of the wearer; and a controller configured to adjust the transmittance of the dimmer filter and the light intensity of a light source of the image display part based on the light intensity of the external light obtained by the light intensity detector; wherein: when the light intensity of the external light is within a first light intensity range, the controller is configured to maintain the light intensity of the light source of the image display part constant, and gradually reduce the transmittance of the dimmer filter as the light intensity of the external light becomes higher; when the light intensity of the external light is within a second light intensity range higher than the first light intensity range, the controller is configured to maintain the transmittance of the dimmer filter constant, and gradually increase the light intensity of the light source of the image display part as the light intensity of the external light becomes higher; and characterised in that: a light intensity ratio is controlled to be comparatively higher if the image is composed of intermediate gradations, and comparatively lower if the image is composed of two gradations, wherein the light intensity ratio is defined as C / B, where C is the light intensity of the image transmitted from the image display part, and B is the intensity of the external light reaching the eye of the wearer. when the light intensity of the external light is within a first light intensity range, the controller is configured to maintain the light intensity of the light source of the image display part constant, and gradually reduce the transmittance of the dimmer filter as the light intensity of the external light becomes higher; when the light intensity of the external light is within a second light intensity range higher than the first light intensity range, the controller is configured to maintain the transmittance of the dimmer filter constant, and gradually increase the light intensity of the light source of the image display part as the light intensity of the external light becomes higher; and characterised in that: a light intensity ratio is controlled to be comparatively higher if the image is composed of intermediate gradations, and comparatively lower if the image is composed of two gradations, wherein the light intensity ratio is defined as C / B, where C is the light intensity of the image transmitted from the image display part, and B is the intensity of the external light reaching the eye of the wearer.