A plurality of disks are supported and rotated by a spindle motor in a case. A stabilizer is located in the case. The stabilizer has a stabilizer plate which is located between the disks and opposed to surfaces of the disks with gaps therebetween and a plurality of support portions which extend from the stabilizer plate outside the disks, are sandwiched between a bottom wall and a cover of the case, and support the stabilizer plate. A method of assembling the stabilizer plate includes positioning the stabilizer plate over a first magnetic disk and securing a support portion to a bottom wall or surface of the case, positioning a second magnetic disk over the stabilizer plate and then securing an upper cover of the case to the support portion.