It is known that the magnetic shields, between which CPP GMR stacks are sandwiched, can be a source of AMR noise. A hydrogen generator comprises a catalyzing portion 50 having particulate reforming catalyst P, and a combusting portion 5 for heating the catalyzing portion 50, the hydrogen generator being configured to generate a reformed gas containing hydrogen while flowing a material gas containing steam in a direction in which the catalyzing portion 50 extends. The mask further includes a second mask member adapted to connect to the first member having spaced apart top and bottom members and spaced apart side members joined to and integral with the top and bottom members. The above constitution of the invention provides the acrylic rubber composition effective for preventing aluminum fixing while retaining the material properties of acrylic rubber and its excellent characteristics.