This control device for an internal combustion engine is equipped with: an air/fuel ratio sensor; and an engine control device that controls the internal combustion engine according to the output of the air/fuel ratio sensor. The air/fuel ratio sensor is configured so that the applied voltage at which the output current reaches zero varies according to the exhaust air/fuel ratio, and the output current increases if the applied voltage is increased at the air/fuel ratio sensor when the exhaust air/fuel ratio is the stoichiometric air/fuel ratio. When the air/fuel ratio of exhaust gas is to be detected by the air/fuel ratio sensor, the applied voltage at the air/fuel ratio sensor is fixed at a constant voltage, said constant voltage being different to the voltage at which the output current reaches zero when the exhaust air/fuel ratio is the stoichiometric air/fuel ratio, and being the voltage at which the output current reaches zero when the exhaust air/fuel ratio is different to the stoichiometric air/fuel ratio. Thus provided is a control device for an internal combustion engine that uses an air/fuel ratio sensor capable of detecting an absolute value for the air/fuel ratio of exhaust gas even if the air/fuel ratio of the exhaust gas is not the stoichiometric air/fuel ratio.