Disclosed herein relates to an insulating liquid supplying device. More specifically, the insulating liquid supplying device of the present invention includes an insulating liquid tank for receiving insulating liquid, a slot die for discharging insulating liquid to the outside, an insulating liquid header located at the upper part of the slot die, conveying insulating liquid transferred from the insulating liquid tank to the slot die, a pipe connecting the insulating liquid tank, slot die, and insulating liquid header to permit transfer of the insulating liquid, and a transfer pump provided in the pipe to transfer insulating liquid from the insulating liquid tank to the slot die.