PROBLEM TO BE SOLVED: To provide an absorbent article that makes it possible to repeat correct positioning of a sensor with respect to an absorbent article.SOLUTION: An absorbent article comprises an absorber 5 and a rear sheet 2. The absorbent article is used by fixing a planar sensor 7 on the surface side of the rear sheet 2, which is not in contact with skin. A mark 8 indicating an area where the sensor 7 is always arranged properly at least in the width direction thereof can be viewed from the rear sheet 2 side.