Fiber Reinforced Plastics (FRP) have been recently attracting attention as an alternative of metal materials. FRP can reduce the weight lightweight of the automobiles automotive and the environmental loading. In particular, Carbon Fiber Reinforced Thermoplastics (CFRTP) have been studied due to high mechanical properties and short molding cycle. In general, as a method of injection-molding of CFRTP, the thermoplastics and short fibers are kneaded with a twin-screw extruder, and extruded are injected into the mold. It is known that higher mechanical properties can be expected by using long-fiber reinforced thermoplastic (LFT) pellets for injection molding. However, those properties are often insufficient because of unsatisfactory resin impregnation into fiber bundles and poor fiber dispersion in LFT pellets. In the LFT pellets manufacturing apparatus, it was found possible to attain better resin impregnation by spreading carbon bundles with threading them through rollers. However, appropriate conditions affecting fiber opening has not been known. This study revealed the fiber opening mechanism in of LFT manufacturing apparatus. Model apparatus consisting of a series of rollers for spreading carbon bundles was set up, and opening level of fibers passing at each rollers were continuously observed by high-speed movies. The rollers for opening fiber used are non-rotating rollers and rotating rollers. Rotating rollers can spin around shafts by power to pulling fibers. Experiments were conducted in silicone oil as the substitute for molten resin, in addition to the dry state. Rotating rollers were found suitable for opening fibers effectively. Fibers showed better opening in silicone oil than in dry state. The more the number of rollers and the taking-up speed of the carbon bundles were increased, the better fiber opening were. When the contact angle of fibers onto the rollers became larger, the fiber opening tended to decrease.