To facilitate connection with a multi-core connector by reducing spacing fluctuation and aligning difference in level between optical fibers 10a in a coated optical fiber ribbon.

In the collectively coating die device 20 consisting of a nipple 1, a die 2 and a sleeve 3 for manufacturing the coated optical fiber ribbons 10, which are constituted of the optical fibers 10a arranged in parallel on a plane and coating them altogether with plastics, the nipple 1 in the device is provided with a hole 1d for positioning the optical fibers arranged in parallel on the plane, and such device is used in the method of manufacturing the coated optical fiber ribbons 10.