PURPOSE: To make the yield of coating metal high, running efficiency high and product cost low by providing valves in the communicating ports at the front and rear of a continuous ion plating cell, and maintaining the vacuum in the cell even during changing of lots.

CONSTITUTION: Valves 7a, 7b are installed to the communicating ports 6a, 6b between an ion plating cell 1b, an uncoated carbon fiber installing cell 1a and a coated carbon fiber installing cell 1c. An uncoated carbon fiber 4a is installed in the cell 1a, thence the inside of the cells 1aWc are evacuated to about 10-3W10-5 torr. The leading end of the fiber 4a is clamped with a guide chuck 10 and is introduced into the cell 1b. While the fiber 4a moves along a guide rail 9 connected to the cathode of an electrode 3 of 2-5KV, it is plated with the ionized metal 5 generated from a crucible 2 to a coated carbon fiber 4b which is taken up on a roll 8b in the cell 1c.