Cases of charged particle pack ideal focusing in the presence of constant magnetic field have been considered. One-directional ideal space-time focusing was shown to remain only on conditions that a magnetic field being homogenous and its direction being the same as the one of quadratic potential growth. Axially symmetric electrostatic fields with superimposed magnetic field were taken as an example because of their practical importance in the mass spectrometry. It was concluded that at least one equation with separated motion should be linear to maintain the ideal space-time focusing.