Disclosed is a method of treatment with a microwave plasma by maintaining a reduced pressure in a plasma-treating chamber for treatment with a plasma in which a substrate that is to be treated with a microwave plasma is contained, introducing a treating gas into the plasma-treating chamber and introducing microwaves into the plasma-treating chamber, wherein a metallic antenna is disposed in the plasma-treating chamber. The plasma is generated within a very short period of time maintaining stability after the microwaves are introduced into the plasma-treating chamber, and the treatment is accomplished maintaining stability.