Control system of internal combustion engine

A control system of an internal combustion engine comprising:

• an air-fuel ratio sensor arranged in an exhaust passage of the internal combustion engine and detecting an air-fuel ratio of exhaust gas,
• a current detecting device detecting an output current of the air-fuel ratio sensor,
• a voltage applying device applying voltage to the air-fuel ratio sensor, and
• a voltage control part configured to control voltage applied to the air-fuel ratio sensor through the voltage applying device, wherein
• the voltage control part is configured to set the applied voltage to a reference voltage determined so that the output current becomes zero when an air-fuel ratio of inflowing exhaust gas flowing into the air-fuel ratio sensor is a stoichiometric air-fuel ratio, and correct the reference voltage so that the output current detected by the current detecting device becomes zero when it is judged that the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio.