An elevating mechanism includes a cage, a connecting element, a balancing weight body, a sheave and a power output unit. The cage includes an outer box and an inner box. The outer box for containing a fluid has an inlet and an outlet. The inlet is for the fluid flowing into the outer box. The outlet is for the fluid flowing out of the outer box. The inner box is placed inside the outer box for containing a loading body, and suspended in the fluid. The connecting element is wound around the sheave. The power output unit is for driving the sheave. One end of the connecting element is connected to the outer box, and the other end connected to the balancing weight body. The weight of the balancing weight body is equal to the total weight of the outer box, the fluid, the inner box and the loading body.