A Ti50Ni48Fe2 alloy, which is famous as a typical shape memory alloy, exhibits the cubic (parent phase) to trigonal (R-phase) martensitic transformation upon cooling. It is well known that this structural transformation is accompanied by some precursor phenomena, such as appearance of weak diffuse scattering in electron diffraction patterns of the parent phase. Since the diffuse scattering is visible at around 1/31/3 0 and its equivalent positions in diffraction patterns, as similar to the superlattice reflections in the R-phase, it is believed to be closely related with the formation of the R-phase. However, neither structural nor morphological aspect of this pre-martensitic state is clear, since a precise analysis of the weak diffuse scattering is quite difficult along with a conventional electron microscopy, because of the presence of strong background arising from inelastic scattering. The purpose of the present work is to precisely observe the weak diffuse scattering and to reveal the structural and morphological features of the pre-martensitic state by electron microscopy with the aid of a recently developed omega-type magnet.