Abstract: A supporting structure includes two pairs of legs and four wheels each arranged at a lower end of a respective one of the legs. Each leg includes an upper segment and a lower segment, and optionally a retractable leg extension segment for contacting ground instead of the corresponding wheel. Such supporting structure is adapted for producing a lowering motion while keeping the legs crossed on both lateral sides. Such supporting structure may be adapted for assisting a disabled person in travelling on the ground, and also possibly in climbing stairs.