Disclosed is an ion gage using a carbon nano-tube, more specifically a pressure sensor using a field emission of the carbon nano-tube. An array of carbon nano-tubes is formed on a metallic layer. A first grid is disposed on the array of the carbon nano-tubes. A second grid is disposed on the first grid in such a manner as to be spaced apart by a certain desired distance from the first grid. A collector is disposed on the second grid in such a manner as to be spaced apart by a certain desired distance from the second grid. Electrons emitted from the carbon nano-tube are collided with gas molecules to be ionized. The ionized cation is sensed by the collector to be outputted as an electrical signal.