To provide an apparatus for continuously producing vapor-grown carbon fibers capable of simplifying the structure and improving the productivity without choking the lower side of a vertical type furnace core tube by providing a diameter contracting part, etc., having the cross-sectional shape intersecting the axial line at right angles and contracting along the axial line.

This apparatus for continuously producing vapor grown carbon fibers comprises a vertical type furnace core tube 11 having the internal cross-sectional shape in the direction intersecting the axial line at right angles formed into the same in the axial direction, a heating means for surrounding the vertical type furnace core tube 11 so that the interior of the vertical type furnace core tube 11 can be heated, a raw material feeding means 10 for feeding a carrier gas, an organometallic compound as a catalyst and a carbon source gas into the vertical type furnace core tube 11, a gas straightening means for straightening the flow of the gas fed from the raw material feeding means 10 and a diameter contracting part 24 provided in the lower part of the vertical type furnace core tube 11 and having the cross-sectional shape intersecting the axial line at right angles and contracting along the axial line. The diameter contracting part 24 is preferably arranged in the furnace core tube 11 so that the gas flow velocity in the diameter contracting part 24 is 0.8 VO to 20 VO for the gas flow velocity VO in a soaking region uniformly heated in the furnace core tube 11.