To provide a noise reducing circuit which can reduce unnecessary radiation noise generated by a semiconductor device and a semiconductor device equipped with it as to a noise reducing circuit which is suitably used for on board electric accessory equipment requiring EMI countermeasures and a semiconductor device equipped with it.

An LSI chip 1 has a power terminal 4 for supplying an external source voltage to an internal circuit 2 having a circuit operating in synchronism with a clock and a ground terminal 6 applying a ground potential. Further, the LSI chip 1 is equipped with plural low-pass filters LPF which are inserted between the power terminal 4 and internal circuit 2, and the ground terminal 6 and internal circuit 2 and composed of resistance elements RS1 to RSn and RG1 to RGn and MOS capacitors CS1 to CSn and CG1 to CGn, and has a noise reducing circuit which reduces radiation noise conducted from the internal circuit 2.