As there have been many researches for bolt self-loosening and a lot of knowledge have been accumulated, the phenomena has been understood more and more clearly. On the other hand, it is quite difficult to achieve both non-self-loosening and easy bolting tasks. In practical situations, easy and stable bolting is more focused and torque control is employed for tension control in the fields. For the stable bolting, friction of the threads is reduced by lubrication. However, the effect of this friction reduction is not yet investigated in the aspect of self-loosening. In this paper, the effect of frictions between male and female threads and between nut and bearing surface is investigated by FEA simulations. This provides information how self-loosening can be controlled. In this paper, the motion of the fastened plate transverse to the bolt axis is considered. This motion is known as the easiest motion to make self-loosening in experience and also as shown so in the author’s previous researches. The friction seems to increase self-loosening and also decrease self-loosening at the same time. It seems that the friction on the bearing surface drives self-loosening and friction on the thread surfaces prevents it. In this paper, both the frictions are examined in the relative manner with the Finite Element Analyses.