A knocking treatment method in a flat-type display device in which a first substrate provided with a first electrode and a second substrate provided with a second electrode are disposed with a vacuum space interposed between the first and second substrates and the first substrate and the second substrate are bonded to each other in their circumferential portions, the method comprising applying to the first electrode a pulse voltage V₁ higher than a voltage to be applied to the second electrode to remove a projection present in the first electrode by field evaporation.