A defrosting device includes a heating unit filled with a working fluid and including an active heating part heated to a first temperature that can evaporate the working fluid, and a passive heating part positioned at a rear side of the active heating part and heated to a lower temperature than the first temperature. The defrosting device also includes a heat pipe disposed adjacent to an evaporator to transfer heat to the evaporator while circulating working fluid heated by the active heating part, the heat pipe including an entrance portion configured to receive working fluid evaporated by the active heating part, and a return portion connected adjacent to the passive heating part and configured to receive working fluid that has condensed after circulating through the heat pipe. Condensed working fluid received at the heating unit first passes through the passive heating part before being reheated at the active heating part.