PURPOSE: To prepare a magnet having excellent magnetic property in a diametric direction, by imparting compression stress in an axial direction by using a die to a billet comprising a polycrystalline Mn-Al-C base alloy magnet which has been preliminarily made anisotropic at a proper temp.

CONSTITUTION: By using a die 2 wherein a cross sectional area vertical with respect to the axial direction of the hollow body of a billet 1 is smaller than the opening area of a bearing part 23 and a conical part 22 wherein a cross sectional area is successively reduced from a container part 21 and reaches the bearing part 23 is provided, the hollow body of billet 1 comprising a polycrystalline Mn-Al-C base alloy magnet to which has been made anisotropic preliminarily is extruded at 530W830°C from the container part 21 to the bearing part 23 by a punch 3 to impart compression stress to the billet 1 in an axial direction to obtain a magnet having excellent characteristics. In this case, the above mentioned compression stress is an absolute value of a logarithmic stress and desirably 0.05 or more.