A film forming apparatus according to an embodiment includes: a process chamber forming a film on a substrate; an abatement device detoxifying a first exhaust gas exhausted from the process chamber; a first supply pipe for supplying a gas containing water to the process chamber; a first vacuum pump provided in a first flow path of the first exhaust gas between the process chamber and the abatement device; a second vacuum pump provided in the first flow path between the first vacuum pump and the abatement device; and a first detector provided in the first flow path between the second vacuum pump and the abatement device and capable of detecting a hydrogenated gas.