This invention relates to a wide-write/narrow-read head having a pair of C-shaped cores one of which is used as a read core and the other of which is used as a write core, and a closure core which is provided between the two cores to shut off side magnetic circuits at the time of data reading, and provides a magnetic head which further includes an element to either offset magnetic flux of said side magnetic circuits or shorten the magnetic path length thereof or to increase magnetic resistances from said closure core to said read core in order to prevent the magnetic flux extending between said write core and said closure core from leaking into said read core from said closure core. This invention also provides a data recording/reproducing method which can offset magnetic flux of the side magnetic circuits at the time of data reading by forming a magnetic flux in said closure core in the opposite direction, and which can suspend such offsetting operation at the time of data writing by a simple ON/OFF switch.