Vehicles modified with a wheelchair transporting apparatus are generally used for improving wheelchair users'' mobility. However, in designing the apparatus, consideration for passengers'' discomfort and fatigue is not sufficient. As a countermeasure of this problem, both vibration characteristics of the passenger-wheelchair system and passengers'' sensitivity need to be studied. In previous study, authors constructed a vibration simulation model to predict vibration on passengers'' body from floor vibration. This study aims to clarify the relationship between vibration and comfort, and to propose a method to support designing WTA by the findings of this study.First, we carried out a vibration experiment with a vibration generator that vibrated the passenger-wheelchair system and measured floor vibration, vibration on the human body, and subjective evaluation.Second, we discussed experimental results. The result of riding comfort measurements proved that the characteristics of sensitivity to vibration differ in two frequency ranges: from 2 Hz to 6 Hz and from 6 Hz to 12 Hz. Therefore we divided the results into two sections for these two frequency ranges.Relationship between floor vibration and riding comfort was examined. We carried out the multiple regression analysis and deduced the formulas that express the value of riding comfort by the acceleration and frequency of the vibration on the floor.Next, relationship between body vibration and riding comfort was examined. From the result of correlation analysis and multiple regression analysis, vertical vibration on the upper torso is found to be most closely related to the riding comfort. Regression formulas that express the value of riding comfort by the acceleration and frequency of the vertical vibration on the upper torso were deduced.Finally, we proposed a vibration evaluation model that can predict riding comfort from the vertical vibration on the upper torso, which will be valuable in designing the wheelchair transporting apparatus.