To smoothly and surely perform the work of interlocking a fastener consisting of male and female interlocking claws by allowing the female interlocking claw held by a rotor to be guided while keeping a predetermined position, and guiding the male interlocking claw between the outside and inside interlocking claws of the female interlocking claw by means of another rotor.

Male and female interlocking claws 5, 3 at one end of a fastener are interlocked with each other, and at one end of this interlocking part where the male and female interlocking claws 5, 3 are interlocked a fin-shaped thick- wall part 4 is inserted into a guide groove 12a in a first rotor 12. A jig is moved along the longitudinal direction of the fastener. Therefore the first rotor 12 rotates, holding the female interlocking claw 3 in a predetermined position to guide it. The male interlocking claw 5 not yet interlocked is guided between the outside 3a and inside 3b interlocking claws of the female interlocking claw 3 by a second rotor 15 to securely interlock the male and female interlocking claws 5, 3 with each other over the entire length of the fastener.