The slit coater method is an excellent liquid crystal (LC) alignment control technique that can order the LC alignment even on plastic substrates without pre-forming optional LC alignment films. However, controlling an arbitrary pretilt angle is still one of the issues. To elucidate the essence of the mechanism of the alignment transition from the planer to vertical alignment by UV polymerization, an in-liquid atomic force microscope was introduced. As a result, it was deduced that the LC alignment transition is induced by the realignment of mesogenic groups rather than surface topological change.