A high-pressure processing apparatus includes a processing vessel including a processing chamber formed therein to perform a certain process onto an object in the processing chamber; fluid feeding means which feeds a high-pressure fluid into the processing chamber; fluid discharging means which discharges the high-pressure fluid from the processing chamber; an agitating unit which is arranged in the processing chamber and is operative to flow the high-pressure fluid over the object by relative rotation to the processing vessel; a communicating channel which is formed in the processing vessel to communicate inside and outside of the processing chamber; a rotary driving member which is coupled to the agitating unit via a shaft portion provided in the communicating channel; and a sealing portion which is provided between the shaft portion and the processing vessel to disconnect the processing chamber from the rotary driving member. The fluid discharging means includes a fluid discharging port formed in a certain position of the communicating channel closer to the processing chamber than the sealing portion to discharge the high-pressure fluid.