To provide a magnetoresistance effect element which can stably write information by efficiently utilizing a magnetic field which is formed by a current that passes through a writing line, and to provide a magnetic memory device.

An arrangement is made so that areas of cross sections orthogonal to the peripheral directions of a pair of magnetic yokes 4a, 4b become the smallest at coupling portions 14a, 14b which face stacks S20a, S20b, respectively. Thus, magnetic flux density of circulating magnetic fields 16a, 16b caused by passing a writing current through writing bit lines 5a, 5b and a writing word line 6, can be made the highest at the coupling portions 14a, 14b, thereby enabling efficient and stable writing of information.