and increase the bulk density of carbon fiber a packed layer of carbon fiber is compressed a packed layer of carbon fiber is preferably compressed so as to have a volume which is about u00bd or less that before compression subsequently a shut off valve is opened and the compressed layer is intermittently removed through the valve alternatively the compressed layer of carbon fiber may be continuously removed without use of a shut off valve by extrusion through an outlet having a squeezed head portion when a packed layer of carbon fiber is compressed so as to have a volume which is in excess of u00bd that before compression the layer has a large volume of interfiber space thus when the layer is continuously removed gas in the layer cannot be separated sufficiently permitting gas to accompany the carbon fiber product specifically a pressure for compression is 0 1 kg cm 2 or more preferably 1 0 kg cm 2 or more when the pressure is less than 0 1 kg cm 2 gas held between filaments of the carbon fiber is insufficiently separated the pressure may be higher preferably to the extent that carbon fiber does not collapse when the pressure becomes higher facility cost of the pressurizing system becomes higher therefore the pressure preferably falls within a range of 0 1 100 kg cm 2 more preferably 1 100 kg cm 2 still more preferably 1 50 kg cm 2 the process by use of purge gas may be.