A magnetic recording medium is provided on a rotary drum (Lxa) and is divided into a plurality of magnetic tracks (M). On each track (M) is recorded a magnetic signal of a combination of a magnetization portion (SM) which consists of two consecutive unit magnets (pitch λ) and a no-magnetization portion (6b, 7b, 8b) having the same length (2 λ) that are alternatingly arranged over the whole periphery of the track (M). First magnetoresistive elements (R) in the magnetic sensor (5a) are arranged in pairs so as to be opposed to the magnetic tracks maintaining a distance of λ/2. Second magnetoresistive elements opposed to the magnetic track that corresponds to the lowest-order bit of position detecting signals, are arranged in a number of 2m for the first magnetoresistive element maintaining a distance of 1 +2n ( ) SM L where SM L denotes the length of the mag- netic signal of the magnetic track, m denotes the number of the increased bits, and n denotes an integer. Thus, detecting signals are obtained in a bit number in excess of the number of the magnetic tracks (M).