A layer formation method is disclosed which comprises supplying gas to a discharge space, exciting the supplied gas at atmospheric pressure or at approximately atmospheric pressure by applying a high frequency electric field across the discharge space, and exposing a substrate to the excited gas, wherein the high frequency electric field is an electric field in which a first high frequency electric field and a second high frequency electric field are superposed, frequency .omega..sub.2 of the second high frequency electric field is higher than frequency .omega..sub.1 of the first high frequency electric field, strength V.sub.1 of the first high frequency electric field, strength V.sub.2 of the second high frequency electric field and strength IV of discharge starting electric field satisfy relationship V.sub.1.gtoreq.IV>V.sub.2 or V.sub.1>IV.gtoreq.V.sub.2, and power density of the second high frequency electric field is not less than 1 W/cm.sup.2.