A part positioning apparatus comprises a target marker (2a) provided on a tip end of a wire (2b) to be set on a motor vehicle body (W), a sensed member for accommodating the wire (2b) in such a state as to be pulled out and wound up, a first sensor (3) for detecting a pulled-out length of the wire (2b) when the target marker (2a) is set on the motor vehicle body (W), a second sensor (4) for detecting an existing location of the wire (2b) when the target marker (2a) is set on the motor vehicle body (W), and a controller means (5) for controlling a traveling amount of the self-traveling machine (1) such that each of detection values of the first sensor (4) and the second sensor (5) becomes a given value.