An MR sensor for a card reader structured to detect whether or not magnetic data are recorded in a magnetic stripe of a card, which is provided with the magnetic stripe in which magnetic data are capable of being recorded in a first track and magnetic data are capable of being recorded in a second track, the MR sensor comprising: a first resistor and a second resistor which are serially-connected with each other and are disposed at positions where the first track is passed; and a third resistor and a fourth resistor which are serially-connected with each other and are disposed at positions where the second track is passed, the MR sensor being characterized in that the first resistor and the second resistor are formed line-symmetrically with respect to a first imaginary line parallel to a first direction which passes a center position in a passing direction between the first resistor and the second resistor when viewed in a second direction, and that the third resistor and the fourth resistor are formed line-symmetrically with respect to a second imaginary line parallel to the first direction which passes a center position in the passing direction between the third resistor and the fourth resistor when viewed in the second direction, wherein the second resistor and the fourth resistor are connected with a power supply, and the first resistor and the third resistor are grounded, wherein a potential difference between a first midpoint between the first resistor and the second resistor serially-connected with each other and a second midpoint between the third resistor and the fourth resistor serially-connected with each other is an output of the MR sensor wherein the first imaginary line and the second imaginary line are disposed on a same straight line. a first resistor and a second resistor which are serially-connected with each other and are disposed at positions where the first track is passed; and a third resistor and a fourth resistor which are serially-connected with each other and are disposed at positions where the second track is passed, the MR sensor being characterized in that the first resistor and the second resistor are formed line-symmetrically with respect to a first imaginary line parallel to a first direction which passes a center position in a passing direction between the first resistor and the second resistor when viewed in a second direction, and that the third resistor and the fourth resistor are formed line-symmetrically with respect to a second imaginary line parallel to the first direction which passes a center position in the passing direction between the third resistor and the fourth resistor when viewed in the second direction, wherein the second resistor and the fourth resistor are connected with a power supply, and the first resistor and the third resistor are grounded, wherein a potential difference between a first midpoint between the first resistor and the second resistor serially-connected with each other and a second midpoint between the third resistor and the fourth resistor serially-connected with each other is an output of the MR sensor wherein the first imaginary line and the second imaginary line are disposed on a same straight line.