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