A magnetic device comprises two base portions and magnetic pillars, wherein each of the two base portions has a first surface and the two first surfaces are faced to each other, and the magnetic pillars are disposed between the two first surfaces along a first direction, wherein, in the first direction, two of the magnetic pillars located at the outermost side of the base portion are a first corner pillar and a second corner pillar respectively, n of the magnetic pillars having the same cross-sectional area and located at the center position of the base portion are n center pillars, and cross-sectional area of the magnetic pillars are gradually increased from the first corner pillar to the center pillar closest to the first corner pillar, and from the second corner pillar to the center pillar closest to the second corner pillar.