PURPOSE: To impart a flow property to a latent heat accumulating medium even if this medium becomes cool.

CONSTITUTION: This latent heat accumulating medium 12 encapsulated in a hermetic bag 11 is formed by polyethylene (PE) glycol 13 as a latent heat accumulating material into many capsules 14 and immersing these many capsules 14 into water 15 which is liquid having the melting temp. lower than the melting temp. of the latent heat accumulating material (PE glycol 13). The PE glycol 13 in the respective capsules 14 solidifies by cooling but the water 15 which immerses the capsules 14 maintains the flow property and, therefore, the respective capsules 14 are freely movable in the water 15 and the flow property adequate as a whole of the latent heat accumulating medium 12 is maintained even if the PE glycol is cool. The heat accumulating bed warmer 10 is, therefore, deformable according to the movement of the human body by movement of the capsules 14 in the water 15 even if the PE glycol 13 which is the latent heat accumulating material cools to solidify. The touch to the skin and the feel of fitting of the heat accumulating bed warmer 10 is improved.