A buried-magnet internal rotor (1) for an electric rotating machine, the rotor including a shaft (2), a plurality of polar parts (30) made of a magnetic material surrounding the shaft, the polar parts delimiting housings (40) between them, a first lateral shroud (5) and a second lateral shroud (5′) axially on each side of the polar parts along the shaft (2), the shaft passing through each lateral shroud through a central opening in each lateral shroud, at least one tie-rod (6) per polar part, the tie-rod clamping each polar part between the lateral shrouds, permanent magnets (4) placed in the housings (40), wherein the shaft includes, for the first lateral flange (5), an internal shoulder (22) designed to form an axial abutment against which the first flange is held axially by an external ring (26) secured to the shaft.