8. A voice recognition method for recognizing keywords included in input voice, comprising: a first step that generates a recognition hypothesis graph which indicates a structure of hypothesis that is derived according to said first grammar together with a score associated with respective connections of a recognition means by executing a voice recognition process based on said first grammar to a voice feature amount of input voice; and a second step that outputs a recognition result from a total score of a hypothesis which is derived according to said second grammar after acquiring said structure and said score of said garbage section from said recognition hypothesis graph, and executing said voice recognition process according to said second grammar that is specified to accept a section other than keywords in input voice as said garbage section to said voice feature amount of input voice, wherein selecting no smaller than one voice section having a node which can connected with said hypothesis as a starting point in said recognition hypothesis graph and connecting said structure and said score of said selected voice section with said hypothesis as said structure and said score of said garbage section, to said hypothesis reached to said garbage section in said second grammar, in said second step.
13. The voice recognition method according to claim 8 , wherein executing said voice recognition process in a reverse direction with time direction of input voice in said second step.