A watch intended to be removably mounted on a support, including a watch case and an independent removable attachment device arranged to retain the watch case in an opening provided in the support, the watch case including an upper portion, on the dial side, and a lower portion including a back cover, the lower portion being arranged to be housed inside the opening in the support and being of smaller dimensions than those of the upper portion to form a flat peripheral shoulder. The attachment device includes a flange having a central opening arranged to receive the lower portion of the watch case and an inner rim delimiting the central opening, the inner rim being arranged to be housed inside the opening in the support. The inner rim includes a locking device for locking the attachment device on the lower portion of the watch case.