To easily mount a bolt to a hub shaft comprising bearing device with proper attitude.

In this bolt mounting aid tool 40 used upon press fitting the bolt 10 to a through-hole 24 of a flange 21 of the hub shaft 2, the bolt 10 is guided with a centralshaft P of the bolt 10 kept in the attitude approximately parallel to a central shaft O of the hub shaft 2 in the press fitting process. By using this bolt mounting aid tool 40, the bolt 10 can be press fit with the proper attitude to the through-hole 24 regardless of whether an area used as a bearing surface of the bolt is smooth or not in the flange 21. Thereby the smoothing machining of the area used as the bearing surface of the bolt 10 in the flange 21 in a conventional case, becomes unnecessary.