A controller (3) of an air-fuel-ratio sensor (100) according to an embodiment includes a current supplying unit (13), a sweep processing unit (16), and an abnormality detecting unit (20). The current supplying unit (13) supplies a current (Ip) to the pump cell (4) through a first terminal (Tip) connected with the pump cell (4) so as to control the pump cell (4). The sweep processing unit (16) executes a sweeping process in which a predetermined voltage (Vm) or a predetermined current (Im) is applied to the detection cell (5) through a second terminal (Tvs) connected with the detection cell (5) so as to change a voltage (Vs) and a current (Is) of the detection cell (5). The abnormality detecting unit (20) detects a shortcircuited state between the first terminal (Tip) and the second terminal (Tvs) on the basis of a fluctuation in a voltage (Vp) or a current (Ip), generated by the sweeping process, of the first terminal (Tip).