PURPOSE: To eliminate the mismatching of the transmitting situation of the transmission shift register of a serial interface device with a software processing by a CPU at the time of moving from a macro-service function processing to a vector interruption processing.

CONSTITUTION: In a serial interface device 3', the data of an inside bus 4 are set in a transmission shift register 31 by a transmission start signal ST, and the data are shifted by a serial clock signal CLK, and serially outputted to an output terminal OUT. A transmission end detecting circuit 33 detects the empty of the transmission shift register 31, and transmits a request signal REQ. An RS flip flop 34 is set by the transmission start signal ST, and reset by the request signal REQ, and a transmission end flag FLG is generated.