1. A computer-readable information storage medium that stores a program for generating Hidden Markov Models to be used for speech recognition with a given speech recognition system, the information storage medium storing a program that renders a computer to function as: a scheduled-to-be-used model group storage section that stores a scheduled-to-be-used model group including a plurality of Hidden Markov Models scheduled to be used by the given speech recognition system; and a filler model generation section that generates Hidden Markov Models to be used as filler models by the given speech recognition system based on all or at least a part of the Hidden Markov Model group in the scheduled-to-be-used model group.