Disclosed is a substrate processing apparatus including a processing vessel in which a target substrate W is processed by using a high-pressure fluid in a supercritical state or a subcritical state, and pipes that are divided into a first pipe member and a second pipe member in a flowing direction of the fluid and circulate the fluid are connected to processing vessel. A connecting/disconnecting mechanism moves at least one of first and second pipe members between a connection position and a separation position of first pipe member and the second pipe member, and opening/closing valves are installed in each of first and second pipe members and are closed at the time of separating pipe members.