An air-fuel ratio sensor control unit connected with an air-fuel ratio sensor including a common terminal, a first terminal and a second terminal includes a common connection terminal connected with the common terminal, a first connection terminal connected with the first terminal, a second connection terminal connected with the second terminal, a voltage control circuit controlling a voltage of the first connection terminal, a resistor connected with the common connection terminal, a voltage sensing circuit sensing a two-end voltage of the resistor, a current applying circuit applying a constant current to the second connection terminal, and a determining unit sensing a change quantity of the two-end voltage by using the voltage sensing circuit and determining whether a disconnection failure of the first connection terminal occurs based on a sensing result of the change quantity.