Plasma treatment device

This plasma treatment device comprises: a plasma treatment chamber; a substrate support; a lower electrode; a RF power source; and an upper electrode assembly. The upper electrode assembly is provided with a gas diffusion plate, an insulating plate, and an upper electrode plate which has a plurality of first through-holes and a plurality of second through-holes and is disposed between the gas diffusion plate and the insulating plate. The insulating plate has an inner annular projection part and an outer annular projection part projecting downward from the lower surface, and the insulating plate has a plurality of first gas introduction holes, a plurality of second gas introduction holes, and a plurality of third gas introduction holes.