To provide a radiation cooling/heating device which can make room cooling and heating with conserved energy by reducing the heat loss of a dehumidifier.

This radiation cooling/heating device transfers the heat of a refrigerant circulating path 5 to a liquid circulating path 4 by means of a heat exchanger 16 for liquid, cools or heats the inside of a room by means of a ceiling radiation panel 3 installed to the liquid circulating path 4, and adjusts the temperature in the room by means of a dehumidifier 24 in which a heat exchanger 14 and a reheater 19 are arranged at an interval in the air blowing and sucking direction of a fan 25. The dehumidifier 24 is constituted by installing an auxiliary heat exchanger 22 for liquid to the liquid circulating path 4 between the heat exchanger 14 and reheater 19.