PURPOSE: To prevent the occurrence of breaks of a liquid, by minimizing the gap between a pair of developing rollers in both end parts and increasing this gap smoothly and maximizing it in the center part.

CONSTITUTION: Both ends of the first roller 1 consisting of a highrigidity metal are held freely rotatably by small-diameter shaft parts 11 and 12. A metallic second roller 2 where the diameter is smaller in a center part 29 is held freely rotatably by shaft parts 21 and 22 in both ends, and both rollers 1 and 2 are interlocked with each other and are rotated by gears 41 and 42. Since a wide passage 35 for a liquid is formed in the center part 29 of both rollers 1 and 2, the occurrence of breaks of the liquid is prevented.