1. A speech recognition system, comprising: a first information processing device comprising a speech recognition processing unit for receiving data to be used for speech recognition transmitted via a network, carrying out speech recognition processing, and returning resultant data representative of a result of the speech recognition; and a second information processing device: which is configured to respond to input sound data and which is connected to the first information processing device via the network, which performs mapping of the input sound data by using a mapping function which processes mathematically the input sound data and which is unknown to the first information processing device to obtain mapped data, which transmits the mapped data to be used for the speech recognition by the speech recognition processing unit to the first information processing device; which receives the resultant data concerned with the mapped data from the first information processing device, and which constructs a speech recognition result, based on the mapping function used, from the resultant data returned from the first information processing device into the same result as a result of performing the speech recognition without using the mapping function; wherein: the input sound data comprises an acoustic model, a language model or feature vectors, and the mapping of the input sound data is performed by mapping the structure of at least one of them; phoneme IDs which are indices to phonemes included in the acoustic model are mapped by using the mapping function; phoneme ID strings indicating pronunciations of respective words included in the language model are mapped by using the mapping function; and at least information on representation character strings of the respective words included in the language model is deleted.