To equally insulate the cold of the remains stably placed in a coffin without using any dry ice.

Concerning a flat casing 1 to be used while being freely attachably and detachably set to a coffin B in which the remains are stably placed, an internal hollow 2 fixedly divided into a warm air passage part 2a and a cold air passage part 2b, a heat exchanger 4 is arranged at a boundary part 1a, a pair of cooling medium pipes 5 are connected to this heat exchanger 4, a cold air blowing port 6 is formed on a lower face 1b of the cold air passage part 2b, and a fan 7 for circulating air in the coffin is arranged on it. Then, an observation window part 3 is formed at the terminal part of the warm air passage part 2a, and a warm air sucking port 8 provided with a filter 9 is formed on the lower face 1b of the warm air passage part positioned just between the observation window part 3 and the boundary part 1a.