a mounting table for supporting the processing object thereon;

a high pressure chamber adapted to contain the processing object therein, the high pressure chamber having a top wall positioned above an entire surface of the processing object on the mounting table and including a fluid introduction passage connected to a source of fluid at a high pressure of at least 1 MPa for introducing the high pressure fluid into the high pressure chamber, the high pressure chamber further having a side wall continuous with an outer peripheral part of the top wall and extending down therefrom to surround the mounting table;

a rotating mechanism adapted to rotate the processing object together with the mounting table;

a fluid dispersion mechanism for dispersing the flow of the high pressure fluid to be supplied toward the surface of the processing object from the fluid introduction passage; and

a fluid discharger for allowing the high pressure fluid supplied from the fluid dispersion mechanism to the surface of the processing object, to be distributed radially outward along the surface of the processing object by the rotation of the processing object, and discharged outside the high pressure chamber, the fluid discharger including a fluid discharge passage provided in the sidewall of the high pressure chamber at an outward position relative to the processing object;

wherein the fluid dispersion mechanism includes a closure plate formed with a plurality of through holes and placed between the top wall and the mounting table in opposed relation to the entire surface of the processing object on the mounting table and the top wall, the closure plate being fitted to an internal surface of the side wall of the high pressure chamber so as to make a gap with the top wall and allow the high pressure fluid introduced through the introduction passage to be supplied perpendicular to the surface of the processing object through the gap and each of the through holes.