A method and apparatus for estimating a position and an orientation of a mobile robot. The apparatus includes: a ceiling image grabber for obtaining a ceiling image of an area where the mobile device travels; a mark detector for detecting a retro-reflective artificial mark from the ceiling image, the retro-reflective artificial mark including a first mark and a second mark, each including a non-reflective portion and an infrared reflective portion; and a position & orientation estimator for estimating a position and an orientation of the mobile device using a position of the artificial mark or encoder information according to whether detection of the artificial mark is successful.