When a rotational angle of a pedal is in a range from an angle of zero degrees to a predetermined rotational angle, which is larger than a full-opening-time rotational angle, a first Hall IC outputs a first voltage, which is twice larger than a second voltage outputted from a second Hall IC. When the rotational angle of the pedal is larger than the predetermined angle, the first Hall IC outputs a predetermined constant voltage. When an output difference, which is computed based on the first voltage and the second voltage, is equal to or smaller than a second threshold value, an abnormality of the sensed rotational angle of the pedal is determined.