Abstract: Thermal accumulator (1) comprising external walls (2) delimiting a closed storage space (3) that contains a PCM (4) and a heat exchanger (5) formed by a conduit for fluids having a section (12) inside said storage space (3). Two of said external walls (2) are facing one another and are connected between them by internal walls (10a) located inside the storage space (3) and arranged so that cells (11) containing the PCM (4) are formed in said storage space (3) by said internal walls (10a) and said external walls (2). The external walls (2) and the internal walls (10a, 10b) are flat copper sheets. The section of the heat exchanger (5) that goes inside the storage space (3) is joined to a face of one of said external walls (2) and internal walls (10a). The invention also relates to a refrigerated container for transporting goods comprising the thermal accumulator (1).