The study has attempted to develop a method for estimating modal share of inter-city express trains focusing on mode choice behavior in inter-regional trips. Firstly, the paper indicates that most travelers are mode captive, who recognize only one transportation mode among various alternatives in their mode choice behavior. Thus, an attempt was made in this paper to develop a PLCS (Parameterized Logit Captivity and Selectivity) model to describe mode choice behavior more appropriately. This study also showed that the method developed to estimate modal share with the PLCS model was sufficiently accurate.