A magnetic storage device with a significant reduction in power consumption. The magnetic storage device includes: a yoke which is arranged to cover part of a line extending in an arbitrary direction; and a magneto-resistive element which is arranged in contact with the yoke, thereby forming a closed magnetic circuit. The magneto-resistive element is capable of writing information with a field emanating from the yoke. The magnetic storage device satisfies Iw≦a·R, where R is the magnetoresistance of the yoke, Iw is the write current necessary for the line, and a (mA·H)=6E−11.