A storage device includes a control unit, a first voltage supply unit for supplying a first working voltage to the control unit, N memory units, a second voltage supply unit for supplying a second working voltage to each memory unit, a logic gate, a first voltage detecting unit and a second voltage detecting unit. Once the first voltage detecting unit detects that the first working voltage of the control unit is abnormal, the logic gate outputs a first write protect signal to notify the control unit and control the memory units to enter a write protect mode. Once the second voltage detecting unit detects that the second working voltage of one or more memory units is abnormal, the logic gate outputs a second write protect signal to notify the control unit and control the one or more memory units to enter the write protect mode.