This paper introduces a yield-monitoring system that was developed for a head-feeding combine. If yield variations could be measured during harvesting, data could be used to evaluate management history and provide useful information for planning fertilizer applications and management for the following year. First, we studied the yield-monitoring system and used a hybrid yield-monitoring method that involved an optical sensor and load cell. This monitoring method reduced the measurement error, and was useful in practical applications of site-specific crop management. We then assessed the gap between harvesting and yield-monitoring positions. Yield measured in the grain tank could be converted into yield at the harvesting position by correcting the measured yield with a constant that was determined by the relative position (weighted proportional distribution method) based on the experimental results. Finally, an efficient yield-monitoring system for a head-feeding combine was developed, incorporating our sensing and analyzing methods. It was possible to obtain yield data when normally operating a head-feeding combine that was equipped with our system. The resulting map was equivalent to a yield map generated through quadrate sampling. The estimated error of the system was about 10%.