A displacement mechanism of a tray table mounted on an armrest of a seat, said mechanism allowing to correct the lie angle of said tray table keeping it substantially horizontal, said seat being provided with a displacement mechanism, said displacement mechanism of a tray table providing a lever, hinged in the front-upper zone of the armrest where said tray table is arranged, said lever allowing said tray table to rotate in a longitudinal vertical plane, a hinge, arranged at the end of said lever opposite to the one hinged to the armrest, allowing said tray table to rotate according to an arc of a circle lying in a substantially vertical transversal plane, coupling means, provided under said tray table, and downward facing, when said tray table is in a use position, in proximity of said hinge, said lever being hinged on the armrest.