To efficiently wash yarns without deterioration of the yarn quality by bringing the continuously conveyed yarns which are soaked with a chemical solution into contact with wash water whereby the installation space is saved and workability and maintenance are improved.

Washing water is injected to continuously conveyed yarns 42 which are previously soaked with a chemical solution so that the washing water may perpendicularly collide to the yarns to cover all the surfaces of the yarns 42 with the washing water while conveying the yarns under contact with the washing water. At the area where the washing water collides to the yarns 42, the flow rate of the component perpendicular to the yarn-conveying direction is preferably 0.1-1.0/ms.