A substrate processing apparatus is configured to dry a substrate by replacing a liquid film formed on a top surface of the substrate, which is horizontally held, with a supercritical fluid. The substrate processing apparatus includes a pressure vessel, a cover body and a supporting body. The pressure vessel has therein a drying chamber for the substrate. The cover body is configured to close an opening of the drying chamber. The supporting body is configured to support the substrate horizontally within the drying chamber. The supporting body is fixed to the drying chamber.