A device for attaching an aircraft engine including a rigid structure forming a structure box, and a device for absorbing thrust loads including a main fitting fixedly mounted on one of the spars forming the structure box, by a fixing mechanism. The fixing mechanism includes a fixing peg mounted on the spar and including a main portion located on the outside relatively to the box, the fitting being crossed by the portion of the peg and pressed against the spar by a bell-shaped supporting washer surrounding the main portion and stressed by a screw crossing it, the latter being screwed into a barrel nut housed in a bore made within the main portion.