A semiconductor integrated circuit includes a user circuit and a power supply noise suppression circuit. The user circuit includes a plurality of circuit modules each containing an operation ratio control circuit. The power supply noise suppression circuit judges an amount of current fluctuation occurring in the user circuit by monitoring an operation ratio of each of the plurality of circuit modules, and controls, via each of the operation ratio control circuits, the operation ratio of a corresponding one of the circuit modules in accordance with a result of the judgment of the amount of current fluctuation.