a display unit that is provided inside a housing mounted on a user's head and that displays an image to the user; and

a processor, wherein

the processor detects termination of display by the display unit,

the processor determines an adaptation display pattern that reduces a difference between an internal illuminance value indicating a brightness inside the housing and an external illumination value indicating a brightness outside the housing by changing a brightness of the image displayed on the display unit,

the processor calculates an increased display time of the adaptation display pattern corresponding to a larger illuminance difference between the internal illuminance value and the external illuminance value, and

wherein the processor determines a time change rate of brightness in the adaptation display pattern to be smaller when the internal illuminance value is larger than the external illuminance value as compared to when the internal illuminance value is smaller than the external illuminance value, such that for illuminance differences of identical magnitude, the processor calculates an increased display time of the adaptation display pattern when the internal illuminance value is larger than the external illuminance value as compared when the internal illuminance value is smaller than the external illuminance value.