PURPOSE: To continuously tone a paint with a required color, by sending a predetermined amount of primary color paints having specific colors which was selected by the way conversion of a required three-way valve by change- over signal, to a mixer through a manifold to mix the same.

CONSTITUTION: When an order is applied to a computer 3 so as to issue output corresponding to the toning of a desired paint color, only necessary pumps among pumps 4, 4', 4" are controlled so as to set the number of rotations thereof to a predetermined value. The flow amounts per a unit time of primary color paints recirculated through branched recirculation paths equipped with the pumps concerned are prescribed and the three-way valves in the branched recirculation circuits with the pumps concerned are subsequently opened to a manifold 6 for a definite time under the control by the computer 3. Only a necessary kind of primary color paints are passed through a mixer 7 in a necessary amount and continuously mixed herein to continuously tone a paint with a desired color.