A rotation angle sensor detects a rotation angle of a pedal by its first Hall IC and second Hall IC, which are disposed between two magnets and output voltages varying with magnetic flux changes. When the rotation angle of the pedal is an accelerator full-closure rotation angle or more, the first Hall IC generates a first voltage V1, which is twice as large as a second voltage V2 of the second Hall IC. When the rotation angle is less than 0°, the first Hall IC fixes the first voltage irrespective of the rotation angle. An ECU determines that the rotation angle is abnormal indicating that the pedal rotates in an accelerator closing direction beyond an accelerator full-closure position, when an output difference G1 calculated as G1=V1/2−V2 is more than a predetermined value.