In the vertical magnetic disk unit having a vertical recording medium(13) including a soft magnetic base layer(12) and a vertical recording layer(10) and a recording head including a main magnetic pole(21), a return magnetic pole(22) and exciting coil(23), the product of a magnetostriction constant [lambda] [E-6] of the main magnetic pole(21) and stress S[MPa] acting on the main magnetic pole(21) and coercive force Hc[Oe] of the medium(10) satisfy relation expressed by following expression [lambda]*S>30,000,000/Hc. |