A debugging system includes an emulator connected via a communication line for two-way communication and a target device to be debugged by the emulator. The emulator includes a serial signal transmitting unit to transmit a control signal as serial data to the target device and an A/D converter to convert an analog signal into a digital signal and to output the digital signal, the analog signal is input from the target device via the communication line. The target device includes a trace circuit, a serial signal receiving unit to receive the serial data and a D/A converter to convert, in response to the control signal received, trace information into an analog signal, and to output the analog signal, the trace information is output by the trace circuit.