PURPOSE: To prevent the occurrence of a poor blowing and to improve a product yield, by a method wherein a defoaming tank having a vacuum device is mounted between a blending tank and an intermediate tank of a fiber reinforcing reaction injection system for car component to remove air bubbles adhered to the fiber.

CONSTITUTION: Under a condition that a blending is completed, a composition liquid in an air fuel mixture condition is fed to a defoaming tank 8 through a pipe 4 through the working of a pump 2. When a set quantity of blend liquid is stowed in the defoaming tank 8, a motor 14 runs, an agitating blade 15 is operated, the inside of a vacuum agitating tank 9 of the defoaming tank 8 is brought into a vacuum state by a valve 11 as against a vacuum tank 12 being previously brought into a negative pressure by a vacuum pump 13, and thereby air bubbles included in a composition liquid 16 agitated by the agitating blade 15 are mechanically exfoliated, and sucked and deaired. If air bubbles are reliably deaired, the valve 11 is closed, the motor 14 stops running, the air is introduced, but air dissolution from a liquid surface is not substantially conducted. Then, the deaired blended liquid 16 is fed to an intermediate tank 3 by the pump 2 for storing therein.