A magnetoresistive device has an MgO (magnesium oxide) layer provided between a first ferromagnetic layer and a second ferromagnetic layer. The device is manufactured by forming a film of the MgO layer in a film forming chamber. A substance whose getter effect with respect to an oxidizing gas is large is adhered to surfaces of components provided in the chamber for forming the MgO layer. The substance having a large getter effect is a substance whose value of oxygen gas adsorption energy is 145 kcal/mol or higher. Ta (tantalum), in particular, is preferable as a substance which constitutes the magnetoresistive device.