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The purpose of this study was to develop a hydraulic control system (HCS) as a control unit around which an automatic furrow guidance system (AFGS) for tractor-mounted implements might be developed. The HCS consisted of a hydraulic cylinder slide device, a hydraulic pump, and an electrohydraulic proportional flow and direction control valve (solenoid valve). The basic specifications for the HCS are a hydraulic pressure of 6.8 MPa and flow capacity of 22 L min-1 for the pump, and the fastest speed of the double-acting cylinder, which is mounted to the lower link of a tractor's three-point hitch, needs to be 150 mm s-1. In order to evaluate the basic pressure control characteristic of the HCS, system responses were measured for a step and a simulated crop row input in the laboratory. In field tests, the implement was attached to the three-point hitch linkage of a tractor, with the tractor traveling speed set at 0.5, 1.0, and 1.5 m s-1, to evaluate the crop row and line marker tracking accuracy of the HCS. In the laboratory experiments, the computer needed 0.22 s to calculate and send the control signal to the solenoid valve, which then initiated the hydraulic cylinder movement in 0.07 s. For the frequency response, the cutoff frequency calculated was 0.25 Hz, and the phase delay was 56°. In other words, this guidance system was able to adjust the implements in 3.8 cm s-1. According to earlier research, the maximum adjustment speed permissible for crop row variation was 3.3 cm s-1. The RMS error of the HCS was less than 2.0 cm in tracking the line marker and less than 2.5 cm for crop rows in the field experiments. However, the implement tines did not actually engage the soil in the field experiments. [ABSTRACT FROM AUTHOR]