To provide an object detection device, capable of always acquiring proper information, and its reference axis setting method.

Scanning reference axes, set in each device, are stored in a memory means, in a state with this object detection device for detecting an object by scanning a probing wave and receiving the reflected waves is installed on an installation member, to thereby improve installation work efficiency and reliability. A structure is made such that the state of the installed body is detected, and the scanning reference axis is changed, corresponding thereto, to thereby improve detection accuracy of the object in the proving direction. A reference axis adjusting device, having a reception part and a transmission part for transmitting a reference position signal, is positioned so that its reception part faces straight toward a probing wave transmission means of the object detection device relative to the object detection device; the probing wave of the object detection device is scanned; and the reference position signal is transferred between both devices at the position, where the intensity of the probing wave received by the reference axis adjusting device becomes maximum, thereby to set the scanning reference axis. The axis is stored in the memory means of the object detection device, so as to automate the reference axis adjustment, and to simplify a setting work.