In a watchcase of a time-piece an internal blocking device for simultaneously blocking the push-buttons (10, 20) of the timepiece comprises an internal collar (11, 21) for each push-button pressing a gasket (12, 22) thereof against the watchcase (30) and at least one sliding element (40) providing blocking members (41, 42) for blocking the movement of the push buttons (10, 20). The sliding elements (40) are operated from outside the timepiece through the wind/set crown (50), a specific screw down button, the bezel (60) or other external members of the timepiece. The internal push buttons blocking device of the invention improves watertightness of the timepiece by a simple and reliable mechanism which is very easy and rapid to use.