Data relay method and data relay apparatus

A data relay apparatus (33) has a plurality of conversion process parts (8) installed therein and the plurality of conversion process parts (8) are prepared for respective types of data items transmitted from a first data processing apparatus (31, 32, 41, 42) used as a data transmission source. The conversion process parts (8) are software parts which convert data items of respective types. The data relay apparatus (33) includes a data reception processing section (332) which receives data transmitted from the first data processing apparatus (31, 32, 41, 42), a data conversion processing section (333) which determines a type of data received, retrieves one of the conversion process parts (8) which is prepared for the data and starts the conversion process parts (8), and a data transmission processing section (334) which transmits data converted by the conversion process part to a second data processing apparatus (41, 42, 31, 32).