A brightness correction device equipped with a display unit, comprising: an illumination sensor for measuring an illuminance value that is ambient environment information; a memory (105, 205) for storing a current brightness setting value and calculation information used for calculating a delay time until a brightness correction start time to start updating the current brightness setting value to a target brightness setting value; an illumination controller (102, 202) for determining the target brightness setting value from the illuminance value measured by the illumination sensor, determining the brightness correction start time in response to the target brightness setting value, the current brightness setting value and the calculation information stored in the memory (105, 205), calculating an amount of brightness setting change per specified time based on the current brightness setting value stored in the memory (105, 205) and the target brightness setting value at the brightness correction start time, and outputting an output brightness setting value in response to the amount of brightness setting change that is calculated; and a brightness controller for adjusting brightness of the display unit in response to the output brightness setting value output from the illumination controller (102, 202), characterized in that when the current brightness setting value differs from the target brightness setting value, the illumination controller (102, 202): extends the delay time, if a difference between the current brightness setting value and the target brightness setting value is smaller than a predetermined brightness threshold, the delay time being longer as the difference being smaller; and sets a predetermined value to the delay time if the difference between the current brightness setting value and the target brightness setting value is not less than the predetermined brightness threshold. an illumination sensor for measuring an illuminance value that is ambient environment information; a memory (105, 205) for storing a current brightness setting value and calculation information used for calculating a delay time until a brightness correction start time to start updating the current brightness setting value to a target brightness setting value; an illumination controller (102, 202) for determining the target brightness setting value from the illuminance value measured by the illumination sensor, determining the brightness correction start time in response to the target brightness setting value, the current brightness setting value and the calculation information stored in the memory (105, 205), calculating an amount of brightness setting change per specified time based on the current brightness setting value stored in the memory (105, 205) and the target brightness setting value at the brightness correction start time, and outputting an output brightness setting value in response to the amount of brightness setting change that is calculated; and a brightness controller for adjusting brightness of the display unit in response to the output brightness setting value output from the illumination controller (102, 202), characterized in that when the current brightness setting value differs from the target brightness setting value, the illumination controller (102, 202): extends the delay time, if a difference between the current brightness setting value and the target brightness setting value is smaller than a predetermined brightness threshold, the delay time being longer as the difference being smaller; and sets a predetermined value to the delay time if the difference between the current brightness setting value and the target brightness setting value is not less than the predetermined brightness threshold. extends the delay time, if a difference between the current brightness setting value and the target brightness setting value is smaller than a predetermined brightness threshold, the delay time being longer as the difference being smaller; and sets a predetermined value to the delay time if the difference between the current brightness setting value and the target brightness setting value is not less than the predetermined brightness threshold.