PURPOSE: To send data groups from respective input data generating means from one data line while preventing insertion to one another without increasing the processing burden of a computer device main body to which plural various input data generating means are connected.

CONSTITUTION: When each of input devices A to C adds a start discrimination code S including the classification of data and information of the start and an end discrimination code E including the classification of data and information of the end before and after each data group respectively to send the data group, a signal switching device 4 to which some data group is inputted through input lines La to Lc selects only input data corresponding to information of the classification of data included in the added start discrimination code S till recognition of the end discrimination code E after recognizing the code S and outputs selected input data to an output line Lout.