A chemical heat accumulator includes first- to Mth-stage heat storage units and a condensing part. Each heat storage unit includes a reaction vessel housing first reactant, a container housing second reactant, and a connection passage connecting the reaction vessel and the container for guiding the second reactant from the container to the reaction vessel. The connection passage is provided with an opening/closing member for opening and closing the connection passage. The reaction vessel of the Mth-stage heat storage unit is thermally connected with an object to be heated. The reaction vessel of a (N−1)th-stage heat storage unit is thermally connected with the container of an Nth-stage heat storage unit. M is an integer equal to or greater than 2, and N is an integer equal to or greater than 2 and equal to or less than M.