A device for attaching a bracelet or strap to a watch case includes a bar secured to the watch case by at least one horn and an insert integral with the end of the bracelet. The bar and the insert are complementary to cooperate by interlocking or fitting with each other to form a removable assembly to make the bracelet interchangeable. The bar is formed by a cylindrical shaft having a flat portion, the flat portion being arranged to cooperate by interlocking or fitting with at least one housing made in the insert, the housing having a substantially rectangular opening for receiving the flat portion. The shaft is telescopic to move from a first position, in which the insert is positionable on the shaft, to a second position, in which the insert is locked on the shaft.