To provide a production unit and a production method of gas dissolved water which can operate consecutively and stably ranging over a long period of time.

A first on-off valve 14 is open, a second on-off valve 18 is closed, raw water is circulated from a degassing film module 2 to a liquid phase chamber 4b of a gas dissolving film module 4, and also gas is supplied into a gas phase chamber 4c via gas supply piping 11. This gas supplied into the gas phase chamber 4c permeates a gas permeating film 4a, and is dissolved in raw water inside the liquid phase chamber 4b. When an amount of condensate increases and a water surface is detected by a level sensor 15, a signal is sent from a controller to close the first on-off valve 14 and open the second on-off valve 18. Thus, the condensate reserved in piping 16 is discharged to an ejector 10 via piping 19.