Watch assembly comprising a support, a watch case removable with respect to this support and provided to receive a time counting and display device, as well as a device for assembling two bodies, which are the support and the watch case, this assembly device comprising: - at least one hooking catch, and - at least one retaining portion for the hooking catch, the hooking catch and the retaining portion each being borne by one of the two bodies and being configured to be capable of hooking to each other so as to prevent the watch case and the support from being moved away from each other, the hooking catch and the retaining portion being configured to be able to penetrate each other so as to achieve a locking preventing the hooking catch and the retaining portion from being unhooked from each other without a movement of the watch case and the support towards each other in a locking/unlocking direction, the assembly device comprising at least one resilient member mounted in a first of the two bodies in a way so as to be able to produce a thrust which must be counteracted in order to bring the watch case and the support towards each other into a relative position in which the locking between the hooking catch and the retaining portion is defeated, the assembly device comprising at least one rolling element rotatable on itself, mounted in the first body in a way so as to be movable outwardly into a projecting position under the thrust coming from the resilient member, and to be able to apply this thrust on the second body among the watch case and the support in the locking/unlocking direction, and characterized in that the body comprising the said retaining portion comprises at least one added packing defining a track for the sliding of the hooking catch. - at least one hooking catch, and - at least one retaining portion for the hooking catch, the hooking catch and the retaining portion each being borne by one of the two bodies and being configured to be capable of hooking to each other so as to prevent the watch case and the support from being moved away from each other, the hooking catch and the retaining portion being configured to be able to penetrate each other so as to achieve a locking preventing the hooking catch and the retaining portion from being unhooked from each other without a movement of the watch case and the support towards each other in a locking/unlocking direction, the assembly device comprising at least one resilient member mounted in a first of the two bodies in a way so as to be able to produce a thrust which must be counteracted in order to bring the watch case and the support towards each other into a relative position in which the locking between the hooking catch and the retaining portion is defeated, the assembly device comprising at least one rolling element rotatable on itself, mounted in the first body in a way so as to be movable outwardly into a projecting position under the thrust coming from the resilient member, and to be able to apply this thrust on the second body among the watch case and the support in the locking/unlocking direction, and characterized in that the body comprising the said retaining portion comprises at least one added packing defining a track for the sliding of the hooking catch.