A systematic search for transition state (TS) structures of the chirality-determining elementary step in a RUCl2-((R)-BINAP)-catalyzed asymmetric hydrogenation reaction was performed by using the anharmonic downward distortion following method. As many as 68 TS structures were found for the elementary step because of the complexity of its potential energy surface caused by the introduction of bulky ligands in BINAP for high selectivity. We were able to determine the lowest TS structures for each enantiomer among the 68 TSs, and one for the (R)-type product was found to be the more stable in agreement with the experiment, From a comparison of the lowest TSs for each enantiomer, a "lock-and-key" motif at the TS structure was discovered to be the origin of the high selectivity in the reaction.