PROBLEM TO BE SOLVED: To ordinarily retain a planting part in a fixed position by constantly energizing a float under given pressure in the downward direction and to adjust the planting part by the optimum position and pushing force. SOLUTION: A hydraulic control valve 30 for controlling a hydraulic cylinder apparatus 14 is connected through a sensitivity adjusting mechanism 32 to a float 24. The position of a planting part 20 and the pushing force of the float 24 are controlled based on a soil pressure load acting on the float 24. The sensitivity adjusting mechanism 32 is equipped with a return spring 62 for energizing the hydraulic control valve 30 in the downward direction of the float 24 and an electric motor 63 capable of adjusting the energizing pressure of the return spring 62. When a sensitivity adjusting dial 33 is rotated and operated by fingers, the position of the float 24 is changed through a float sensitivity adjusting wire 45, the length of the return spring 62 is changed by a valve interlocking wire 70 and the pushing pressure of the float 24 is changed. Hydraulic sensitivity is controlled by the changes of the position and the pushing pressure of the float 24.
