In this paper, we introduce a mechanical wheel design capable of step climbing toward more convenient utilization of personal aids such as wheelchairs and walkers. Uneven floors with dips and depressions, thresholds, and steps have still been encountered in our daily routines in spite of the promotion of barrier-free environments. To overcome these difficulties, a step-climbing mechanism and its device are developed, allowing wheeled robots to climb a step where its height is higher than the radius of the wheel. By applying the proposed step-climbing device into a personal aid, its potential users enables to minimize a physical burden during step climbing. As a result, this helps the users live independently and maintain their daily routines, not requiring caregivers and/or medical staff. What is the most important aspect from the practical point of view is how to realize the mechanism without additional wheels and linear guides. This paper describes the mechanical design by controlling axial translation in detail. By using a commercial wheelchair equipped with the proposed device, extensive evaluations are tested and analyzed.