An image display apparatus calculating correction information to correct measured values of an orientation sensor includes an orientation sensor that senses orientation of a viewpoint and outputs measured values, a correction unit for correcting the measured values by using correction information, and a generation unit for generating a virtual image based on the corrected measured values. A display unit displays the generated virtual image, and a calculation unit calculates the corrected information. The calculation unit obtains the measured values of the sensor at the point of when the virtual image is displayed at an appropriate position, generates the correction information from the measured values and predetermined orientation information, and generates the virtual image based on orientation information relating to the viewpoint obtained using the measured values of the orientation sensor and the correction information.