Workload assessment is one of the important elements of the human factors evaluation for the nuclear power plants in operation. This paper describes a further study upon the additional elements of the workload which elements should be considered in the subjective workload assessment. We have tried to predict the burden of the work and to improve the work through a comparison of the objective workload and the subjective workload in the previous studies in nuclear power plants. However, there is a restriction to perform a precise assessment because of the limitations of the method itself. The objective workload assessment is performed by relative comparison using the quadrant analysis with objective workload and subjective workload because there were no clear criteria of objective workload assessment. And the subjective workload assessment is performed by NASA-TLX (NASA Task Load Index) which includes six evaluation dimensions of subjective workload. NASA-TLX is difficult to grasp the other aspects that could influence on the subjective workload because the analysis relies on predetermined assessment items. We conduct a factor analysis between the factors that affect the workload and the assessment adopted from ISO 10075 and NASA-TLX. At the same time, this study suggests other evaluation elements which can be added for subjective workload assessment except for evaluation elements of NASA-TLX.