An active medium piece (109), which has been taken out using a nanoprobe (108), is processed so as to match the shape of a nanoslot (104), and thus an active medium small piece (111) that is smaller than the active medium piece (109) is formed (a fourth step). For example, irradiation with an ion beam (110) is performed so that the active medium piece (109) is shaped (processed) into an active medium small piece (111) that has a three-dimensional shape suitable for being placed in the nanoslot (104). The active medium piece (109) is processed into the active medium small piece (111) in the state of being held by the nanoprobe (108).