To provide a device capable of accurately moving forwards or backwards by automatic driving on a narrow approach ramp using a simple means.

A reflection tape 7 or a magnetic tape 7' is attached along the center line of an approaching direction A of a self-propelled dolly 4 on the lower face of a structure 2, and detectors 8-11 are arranged on the upper face of a body 5 of the dolly 4, and the position of the reflection tape 7 or the magnetic tape 7' is detected by the detectors 8-11, and the signal of the detector 8 is introduced to a drive controller 12 of the self-propelled dolly 4 so that traveling can be controlled. Thus, the positioning of the structure 2 and the self-propelled dolly 4 can be realized in this positioning system of the self-propelled dolly.