A watertight structure for a housing is provided with: a case member comprising a first edge that defines the periphery of an opening a lid member that is arranged so as to cover the opening and that comprises a second edge opposite the first edge, said lid member being fixed to the case member in an attachment/detachment direction that is inclined with respect to a direction that passes through the opening an annular elastic member that is interposed between the first edge and the second edge and that is compressed in the attachment/detachment direction so as to block the gap between the first edge and the second edge when the lid member is fixed to the case member a first part that is formed on the elastic member and arranged on a side on which the gap between the first edge and the second edge becomes narrower when the elastic member is compressed in the attachment/detachment direction and a second part that is formed on the elastic member, that is arranged on a side on which the gap between the first edge and the second edge becomes wider when the elastic member is compressed in the attachment/detachment direction, and that has a larger size in the attachment/detachment direction than the size of the first part in the attachment/detachment direction.Le mécanisme étanche à leau pour boîtier de linvention est équipé : dun élément enveloppe qui possède une première partie bord définissant la périphérie dune partie ouverture dun élément couvercle qui est disposé de manière à recouvrir ladite partie ouverture, qui possède une seconde partie bord sopposant à ladite première partie bord, et qui est destiné à être fixé sur ledit élément enveloppe dans une direction attachement/détachement inclinée par rapport à une direction de passage au travers de ladite partie ouverture dun élément élastique de forme circulaire qui est intercalé entre lesdites première et seconde parties bord, qui est comprimé dans ladite direction attachement/détachement lorsque ledit élément couv
