Position relationship detection system

The invention relates to a positional relationship detection system. A positional relationship between an article holding portion and a transfer position of an article transport vehicle is detected bya simpler configuration. A plurality of detected points R for detecting the distance from a detection reference point in a sensor unit are arranged in a detected unit 4 of a detection object of the sensor unit. The detected unit 4 is provided with a plurality of detected surfaces 40 and is formed three-dimensionally. The plurality of detected surfaces 40 can detect at least two of the group, including a plane relative position showing the relative position of the article holding part relative to the transfer position in a first direction (D1) along a reference surface P0 and a second direction (D2) which is along the reference surface P0 and is orthogonal to the first direction (D1), the inclination of the article holding part relative to the reference surface P0, and the rotation angle of the article holding uni