We developed a navigation system for agricultural vehicles that displays optimum work paths and guides steering to support precision farming. It comprises navigation sensors, including a GPS receiver and an azimuth sensor, and a PC that processes the inputs and displays the information. It is operated via a game controller. The control software supports configuring functions, adjusting settings, displaying results, and recording and managing information. It has functions appropriate for Japanese agriculture, allowing ease of handling and working across multiple fields. To verify its utility, we simulated work using a tractor fitted with it. It improved both work accuracy and efficiency. We confirmed its utility and ease of handling in actual farming work. Trial sales of the navigation system were begun in 2007.