PURPOSE: To obtain the heat accumulating member having a high mechanical strength and capable of being used in a construction material by filling the hollow part of a hollow outer frame material with a light core material and filling gaps of the light weight core material with a heat accumulating material.

CONSTITUTION: A glass fiber reinforced thermosetting resin is formed to consistute a hollow outer frame material 1. Then, a light-weight core material having a specific gravity of less than 1 and having gaps, is placed in the hollow part of the hollow outer frame material. Then, a heat accumulating substance 3 is placed in gap parts of the light weight core material 2 to obtain a heat accumulating member 4.