Locking device for the lid (17) of a washing or drying machine, equipped with a locking mechanism comprising an external latch (3) and an internal latch (2) partially housed inside the previous latch. The external latch (3) is firmly attached to an opening handle (15) and subjected to the action of a torsion spring (4), while the internal latch (2) presents on one side a slanted profile (13), and on the side opposite the slanted profile, a shaped profile (12) suitable for inducing a rotation of the latch (3).