To measure a lateral shift of running magnetic tape caused by a lateral movement of the magnetic tape which occurs while the magnetic tape is running, a fixed write head H1 of a measurement apparatus 10 magnetizes part of the running magnetic tape MT in a section of the apparatus 10 where the magnetic tape MT is free from restriction on lateral movement; a pair of guides 14, 14 in a tape guide unit of the apparatus 10 is located downstream of the fixed write head H1 to restrict the lateral movement of the magnetic tape MT; and a fixed read head H2 reads information recorded on the magnetic tape MT in the tape guide unit.