To provide a fastener, a fastening method and a method of manufacturing a male screw, capable of improving the looseness preventive effect, and capable of reducing reduction in strength of the male screw.

This fastener 1 includes a male screw part 20 having a right-handed screw part 21 having a lead angle θ1 and a pitch P1, and a left-handed screw part 22 formed so as to recess the right-handed screw part 21 and having a lead angle θ2 inclining in the opposite direction of the lead angle θ1 and a pitch P2 larger than the pitch P1, a right nut 31 having a screw part of meshing with the right-handed screw part 21 and a left nut 32 having a screw part of meshing with the left-handed screw part 22.