A timepiece and a tool to separate a back from a middle, which jointly delimit a watch case of this timepiece, inside which a horological movement is housed, this tool having the appearance of a wedge, i.e. an acute-shaped part formed by a first face and a second face which intersect at an angle of less than 90 and which are connected to one another by a rounded portion, the first face of the tool being oriented such that it extends parallel to a mean plane wherein the horological movement is located when an horologist engages this tool between the back and the middle in order to separate this back from this middle, the rounded portion being connected to the second face by a curved portion, the curvature whereof is directed towards the inside of a surface delimited by the first and second faces.