To provide an etching method capable of forming a cavity portion having a large space portion or a complicated structure by etching a sacrifice layer through a very fine etching opening at favorable accuracy in configuration. An etching process of a object is carried out by exposing the object to a processing fluid containing etching reaction seed (the third step S3, the fourth step S4), and then, the pressure in the processing chamber is reduced to make a density of the processing fluid around the object lower than that in the fourth step S4 (the first step S1). While the first step S1 to the first step S4 are repeated, in the third step S3 and the fourth step S4 executed after the first step S1, the processing fluid containing etching reaction seed is newly supplied to the processing atmosphere in which the object is placed to make the density of the processing fluid around the object higher than that in the first step S1.