Abstract: According to one embodiment, a memory device includes a memory cell including a magnetoresistive effect element. The magnetoresistive effect element includes a non-magnetic layer between first and second electrodes in the first direction, a first magnetic layer between the first electrode and the non-magnetic layer, a second magnetic layer between the second electrode and the non-magnetic layer, and a first layer between the second electrode and the second magnetic layer. The first layer includes oxygen and at least one selected from magnesium, transition metal, and lanthanoid, the first layer has a first size in the first direction, the non-magnetic layer has a second size in the first direction. The first size is 1.1 times or more and 2 times or less the second size.