A shedding mechanism on a Jacquard-type weaving loom (M), this mechanism comprising a housing extending according to a longitudinal direction (X100, X200, X300), at least one movable hook , moved in the housing by a knife according to a longitudinal direction between a bottom dead center position and a top dead center position, in or near which the hook can be retained by a selection device which comprises at least - an electromagnet which is mounted and fixed in the housing , and which includes ∘ a ferromagnetic core comprising a first pole face (S122) and a second pole face (S124), these pole faces being offset from each other according to the longitudinal direction (X100, X200, X300), and ∘ a non-magnetic portion integral with the ferromagnetic core - a retaining lever configured to retain the movable hook when this is in or near its top dead center position, the retaining lever being pivotally mounted about an oscillation axis (A144) between a position remote from the electromagnet and a position in contact with the electromagnet, and comprising a ferromagnetic armature that magnetically interacts with the first and second pole faces to control the angular position of the retaining lever about the oscillation axis characterized - in that the non-magnetic portion of the electromagnet comprises a guide surface (S144) for the pivotal movement of the retaining lever about the oscillation axis (A144), this guide surface cooperating with the retaining lever in a direction radial to the oscillation axis (A144) between the remote position and the contact position, and - in that the guide surface (S144) is cylindrical with a circular base, centered on the oscillation axis. - an electromagnet which is mounted and fixed in the housing , and which includes ∘ a ferromagnetic core comprising a first pole face (S122) and a second pole face (S124), these pole faces being offset from each other according to the longitudinal direction (X100, X200, X300), and ∘ a non-magnetic portion integral with the ferromagnetic core ∘ a ferromagnetic core comprising a first pole face (S122) and a second pole face (S124), these pole faces being offset from each other according to the longitudinal direction (X100, X200, X300), and ∘ a non-magnetic portion integral with the ferromagnetic core - a retaining lever configured to retain the movable hook when this is in or near its top dead center position, the retaining lever being pivotally mounted about an oscillation axis (A144) between a position remote from the electromagnet and a position in contact with the electromagnet, and comprising a ferromagnetic armature that magnetically interacts with the first and second pole faces to control the angular position of the retaining lever about the oscillation axis - in that the non-magnetic portion of the electromagnet comprises a guide surface (S144) for the pivotal movement of the retaining lever about the oscillation axis (A144), this guide surface cooperating with the retaining lever in a direction radial to the oscillation axis (A144) between the remote position and the contact position, and - in that the guide surface (S144) is cylindrical with a circular base, centered on the oscillation axis. <EOS>