In the present disclosure, the high-pressure chamber includes a chamber main body including a flat rectangular parallelepiped block of a metal which is formed with a flat cavity that serves as a substrate processing space in which a processing using a high-pressure fluid is performed on a substrate, and the substrate processing space being formed by machining the block from one of faces of the block other than the widest face towards another face opposing thereto. In a case where the cavity is constituted as a through hole, the though hole is provided with a cover configured to open or close the cavity on one side of the through hole, and a second block configured to air-tightly seal the cavity on the other side.