loosened in order that the alternator can be moved 2 next to apply an adequate amount of a tension force on the v belt 2 the adjust bolt 2 is rotated and the first shaft portion 29 is disengaged from the hole 33 thereafter the adjust bolt 23 is rotated in the direction c shown in fig8 and 9 when the adjust bolt 23 stops the rotation the worker stops the rotation of the adjust bolt 23 3 lastly the bolts 13 and 39 are fastened to fix the alternator in the appropriate position according to the above embodiment the neck portion 28 of the adjust bolt 23 is employed as a stopper the compression coil spring 25 may be employed as a stopper instead of the neck portion 28 of the adjust bolt 23 further according to the above embodiment the pitch of the thread provided on the first shaft portion 29 is designed to be equal to that on the second shaft portion 30 however it is possible to set the different pitch on the first shaft portion 29 from that on the second shaft portion 30 for example if the pitch of the thread provided on the first shaft portion 29 is set to be less that that on the second shaft portion 30 the slider 26 further moves in the direction b shown in fig8 by the distance which is obtained by the.