1. A data collecting device communicating with a system including electronic control units controlling various functions to collect function data about the functions, said data collecting device comprising: a list information generating section which, before starting to collect function data, communicates with all the electronic control units in the system to recognize the functions controlled by the electronic control units and generate unit-specific function list information which is a list of the functions categorized by function type and by electronic control unit; a function selecting section which selects at least one function type about which function data is to be collected; and a data collecting section which communicates by using at least one of the electronic control units which corresponds to the at least one function selected by the function selecting section as at least one communication address on the basis of the unit-specific function list information generated by the list information generating section to collect function data about the at least one function corresponding to the selection information, wherein at least one of the functions which is controlled distributively by two or more of the electronic control units in the system is designated as a common function for at least two of the electronic control units, and a representative electronic control unit which is either one of the at least two electronic control units communicates with the other electronic control unit to obtain common function data about the common function, the list information generating section generates the unit-specific function list information containing information on the representative electronic control unit, and the data collecting section, in response to the common function selected through the function selecting section, communicates by using the representative electronic control unit as a communication address on the basis of the unit-specific function list information containing information on the representative electronic control unit to collect the common function data about the common function corresponding to the selection information.