The present invention provides a rare earth based magnet in which the demagnetization rate at a high temperature can be inhibited even if the amount of heavy rare earth element(s) such as Dy and Tb is evidently decreased compared to the past or no such heavy rare earth element is used. The rare earth based magnet of the present invention is a sintered magnet which comprises R2T14B crystal grains as the main phases and the crystal boundary phases among R2T14B crystal grains. The microstructure of the sintered body is controlled by at least containing the first crystal boundary phases and the second crystal boundary phases, wherein the first crystal boundary phases contain at least R-T-M in the ranges of 20 to 40 atomic % for R, 60 to 75 atomic % for T and 1 to 10 atomic % for M, and the second crystal boundary phases contains at least R-T-M in the ranges of 50 to 70 atomic % for R, 10 to 30 atomic % for T and 1 to 20 atomic % for M.