To provide a mounting assisting tool allowing easy positional adjustment of a member to be mounted.

The mounting assisting tool 2 is to mount a sensor in a mounting part 1 and is equipped with a first member 3 located on the sensor side, a second member 4 on the side with the mounting part 1, and a coupling bolt 5 to couple together the first 3 with second members 4. Further the assisting tool 2 is equipped with a locating means 7 to rotationally adjustably locate the relative positioning between the first 3 and second members 4 to an appropriate position in the direction round the coupling bolt 5. The first member 3 has a first inserting hole 3d for inserting a pole P1 and a first fixing means 3e for fixing the pole P1 in the first inserting hole 3d, while the second member 4 has a part to be fixed 4a to be attached to the mounting part 1.