PURPOSE: To form coloring density gradient on the surface of a lens by rotating a motor forward/backward and applying prescribed motion based upon composite motion consisting of the winding and rewinding of a reel transmission system and the eccentric rotation of the reel to a lens holder coupled with the other end of a string through the transmission system.

CONSTITUTION: When the reel winds and rewinds the string 4 by rotating the motor forward/backward, the lens holder coupled with the other end of the string 4 is vertically moved with a small amplitude and a small period and one period for forward/ backward rotation coincides with one cycle of vertical movement. The difference of motion between forward and backward rotation becomes the rotational movement variable of the reel 3 on a disk 1, the general rotating direction of the reel 3 is determined by changing the ratio of forward and backward rotational periods and the reel 3 is reciprocated in a fixed section of the disk 2, so that one period of the reciprocation becomes one cycle for the vertical movement of the lens holder and continuous movement becomes the vertical movement of a large period. In said constitution, composite motion consisting of the vertical movement with a small amplitude and a small period and the vertical movement with a large period is applied to the lens holder, a dipping time and a dripping position in a dyeing bath are controlled to continuously apply dyeing density gradient to the surface of the lens.