A switching device for a transformer allows stable power supply without power interruption when a secondary winding voltage of the transformer is changed in the case of voltage drop on a distribution line due to a load characteristic. The switching device having an uninterruptible power supply function includes a plurality of switches operated by an external signal, a current circulation unit for multiple switches electrically connected to a large-current path of the switches to perform a switch-on function in place of the switches upon switching on and off between the switches, and a control unit electrically connected to the switches and current circulation unit to read voltage values and to apply signals to the switches depending on the voltage values to sequentially switch the switches. Accordingly, the switching device can stably supply power to power consumption sources without power interruption.