PROBLEM TO BE SOLVED: To provide a hardness measurement method which can continuously detect the hardness of a farm field while traveling so as to be able to easily acquire the distribution in hardness of the whole farm field.SOLUTION: A camera 42 is installed on an autonomous work vehicle 1, and images both a predetermined position of a step 81 or a rear wheel 10 of a machine body of the autonomous work vehicle 1 and a farm field face G under the machine body. The height of the step 81 or the rear wheel 10 of the autonomous work vehicle 1 relative to the farm field face G is calculated during the traveling of the autonomous work vehicle 1, so that the hardness of the farm field is measured from the settlement of the machine body relative to the farm field at arbitrary positions.SELECTED DRAWING: Figure 1
