The invention relates to a watch intended to be removably mounted on a support, comprising a watch case and an independent detachable fastening device arranged to hold the box comprising a top part on the dial side and a lower part comprising a bottom, the watch case, the said lower part being designed to be housed in the opening of the support and having dimensions smaller than those of the upper part to form a flat peripheral shoulder. According to the invention, the fastening device comprises a flange having a central opening arranged to receive the lower part of the watch case and an inner flange said central opening, said inner flange being arranged to be housed in the opening of the support. The internal flange has, on its inner wall, means for locking the fixing device on the lower part of the watch case so as to be able to hold the support between the flange and the flat shoulder of the watch case and to allow unlocking of the fixing device of the watch case by application to the flange of a force substantially perpendicular to the flange and directed outwards so as to be able to release the support.