Phase transition from chiral smectic C-alpha phase (SmC alpha*) to smectic C phase (SmC) driven by an electric field is studied from a standpoint of discrete soliton concept, while similar phenomenon occurring at a transition from chiral smectic C phase (SmC*) to SmC is characterized by a condensation of solitons of sine Gordon equation. As a pitch of SmC alpha* without the field is very short, an equation describing a change of a helical structure is difference equation and the soliton excited at the phase transition should be a discrete type. It is shown that for the pitch larger than three layers, soliton density, which is identical to a wave number of the structure, decreases to zero making a devil's staircase as the field is increased. Though the transition is a continuous type and an interaction between discrete solitons is repulsive like the case of SmC*, a range of the interaction is shorter than the one for the continuous solitons. On the other hand, for the pitch smaller than three, the wave number increases reaching a bi-layer structure as the field is increased, and finally at a critical field the bi-layer structure changes to the uniform SmC continuously. Three-layer structure is proved to be marginal at the SmC alpha*-SmC transition.