A data recording/reproduction method for performing a data recording/reproduction process on a flexible optical disk by rotating the flexible optical disk while controlling an axial runout of the flexible optical disk with a stabilizing member that applies an aerodynamic force to the flexible optical disk, and irradiating an optical beam and focusing the optical beam to the flexible optical disk is disclosed that includes the steps of a) generating a first axial runout, b) generating a focus error signal forming an S-curve when the first axial runout is generated, c) determining a position of the optical beam according to the focus error signal, d) generating a second axial runout that is smaller than the first axial runout after step c), and e) conducting at least one of the data recording process and the data reproduction process after step d).