PROBLEM TO BE SOLVED: To miniaturize a planting driving case by providing a specific structure. SOLUTION: This transmission structure for a planting part in a riding rice transplanter is obtained by protrusively arranging a transversely feeding screw 46 on one transverse outer lateral side of a planting driving case 22 installed in the planting part, engaging a piece receiving member fixed to a seedling-carrying platform with a reciprocating screw groove formed in the transversely feeding screw 46, thereby composing a transversely feeding mechanism so as to reciprocate and move the seedling-carrying platform in the transverse direction by the rotation of the transversely feeding screw 46, protrusively arranging a vertically feeding cam shaft 51 on one transverse outer lateral side of the planting driving case 22 on the side where the transversely feeding screw 46 is installed, composing vertically feeding cams 52 attached to the vertically feeding cam shaft 51 so as to come into contact with an operating member arranged in the seedling-carrying platform and drive a vertically feeding device each time the seedling-carrying platform reaches the transverse moving stroke ends, arranging a connecting pipe 71 in an oblong posture connected to the planting driving case 22 and the transversely feeding screw 46 in a mutual parallel posture and installing the vertically feeding cam shaft 51 between the connecting pipe 71 and the transversely feeding screw 46.
