To stabilize the posture of a seedling planting apparatus by a float and to improve soil preparation performance on the surface of a paddy field by the float in a riding type rice transplanter.

The seedling planting apparatus is vertically movably equipped with the float 24 having width ranging from the right to the left rear wheels 2 by setting the interval between the right and left front wheels approximately equal to that between the right and left rear wheels. The bottom parts 24d of the float 24 corresponding to the passage marks of the right front and rear wheels 2 and the bottom parts 24d of the float 24 corresponding to the passage marks of the left front and rear wheels 2 are made higher than the bottom parts 24a and 24c of the float 24 corresponding to the planting positions of a planting mechanism.