A magnetoresistance effect element having good magnetic characteristics by preventing a deterioration, by heat treating, in a reluctance change rate, and a magnetic memory unit provided with this magnetoresistance effect element to provide excellent writing characteristics. A magnetoresistance effect element (1) comprising a pair of ferromagnetic layers (magnetization fixed layer (5) and magnetization free layer (7)) facing each other via an intermediate layer (6) to allow a reluctance to be changed by running a current perpendicularly to a film surface, at least one of the pair of ferromagnetic layers (5, 7) containing an amorphous ferromagnetic material having a crystallizing temperature of at least 623 K; and a magnetic memory unit comprising this magnetoresistance effect element (1) and bit lines and word lines sandwiching the magnetoresistance effect element (1) in a thickness direction.