PURPOSE: To reduce the resin consumption and shorten the color changing time by supplying a stock resin and liquid color micro-encapsuled as a color agent into the material supplying hopper of an injection molding machine at a constant quantity.

CONSTITUTION: Non-colored material resin 9 and black 10 of micro-encapsuled liquid color are supplied into the material supplying hopper of an injection molding machine for manufacturing a colored molding. The stock resin 9 is supplied from the entrance 4a of a cyclone 4 into the hopper 1; however, the micro-capsules 10 containing powdered liquid color is supplied to the lower part of the hopper by means of a constant quantitative feeder 3 provided on the hopper 1 through a joint pipe 13. When the color is changed, a method of washing a prior coloring agent by flowing only the resin stock 9 is not employed, the coloring agent supplied from the constant quantitative feeder 3 is abruptly changed to another color agent, waiting for black of the liquid color in the molding machine to be displaced by red of the liquid color.