To provide a pulley bolt for preventing the looseness of the pulley bolt by obtaining a stable high axial force and the structure of fastened body.

An annular groove 18 for inserting an O-ring around a pulley rotary shaft as a seal member is provided on the boss end surface 16 of a crank pulley 3 and the contact part 21 contacted with the boss end surface 16 of the inside of the groove 18 is provided on the seat surface 15 of the pulley bolt 7 and also a floating flange 6a is formed on the outside of the contact part 21. By this constitution, as the contact part 21 is contacted to the boss end surface 16, the friction radius becomes smaller in comparison with the case in which the outside part of the seat surface 15 is contacted to the boss end surface 16 and a stable big axial force can be obtained and also the invasion of an oil to the contact part 21 from the O-ring 17 and the looseness of the pulley bolt can be prevented.