The rate of magnetic field relaxation in magnetic CP-stars after they emerge from the zero age Main-sequence line is discussed. Data are introduced which indicate a slow increase in the large-scale dipole component of the magnetic field and a simultaneous slow disappearance of its small-scale component. The magnetic field of CP-stars reaches a maximum after 0.2-0.5 times their lifetime. Data are introduced to support the assumption that the large-scale magnetic field of CP-stars vanishes at the end of their time in the Main sequence because convection develops in the corresponding phases of their evolution. There are indications that the observed dependence of the magnitude of the field on the rotation period of CPstars largely reflects a similar dependence in the protostellar clouds.
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