Substrate processing device, substrate processing method, method for manufacturing semiconductor device, program, and exhaust system

In the present invention, an atmosphere close to a desired process condition can be constructed even when an exhaust system transitions to a prescribed state, and the deterioration of characteristics of process results is suppressed. An invention is provided having: a first gas supply line that supplies a first gas to a substrate in a processing chamber; a first exhaust line that exhausts the first gas; a first valve provided in the first exhaust line; a second gas supply line that supplies a second gas to the substrate in the processing chamber; a second exhaust line that exhausts the second gas; a second valve provided in the second exhaust line; and a control unit that can control the first valve and the second valve so as to perform a first line change process for exhausting the first gas via the second exhaust line when it is detected that the first exhaust line has transitioned to a prescribed state.