To mount and demount mounting brackets for attachments such as the buckets, breakers, etc. of each maker even when distances among the pins of the mounting brackets differ.

The working-machine attachment fixture has a first pin 8 being fixed at one ends of the brackets 7a, 7b of an attachment and having a notched section 8a and the hook section 1a of a coupler 1 inserted and engaged to the notched section 8a of the first pin 8. The fixture has rotatable coupler links 2, in which one ends are connected to working-machine front links 6 through the coupler 1 and the other ends are coupled into mounting holes formed at the other ends of the brackets 7a, 7b of the attachment by a second pin 9.