PURPOSE: To prevent invasion of noises, malfunction and circuit destruction caused when an analog signal processing section and a digital signal processing section are mixed in a semiconductor integrated circuit in the signal processor having the semiconductor integrated circuit.

CONSTITUTION: An A/D converter 11, D/A converters 113, 115 as an analog signal processing section and a digital signal processing section 111 are provided in a semiconductor integrated circuit 6 and the power supply for the respective processing sections is supplied via an independent path. Furthermore, the circuit 6 is provided with buffers 102-106, 108-110, 112, 114, 116-121 to prevent a fault current from flowing between the analog signal processing section and the digital signal processing section at application of power.