The invention regards a locking device for the closing door of a washing and drying machine, constituted of a body of containment (1) that houses a locking wheel (3) for the door latch, subject to the action of elastic means (4), a sliding bolt (5) capable of preventing the rotation of said wheel (3) and a time-delay mechanism fitted with a locking pawl for said sliding bolt (5). The wheel (3) is fitted with a cavity (10) that presents a surface (11) tilted with respect to the plane of rotation, so as to resolve the force it exerts on the bolt (5), when a pulling is exerted on the door (1) while the device is in a closed and locked position.