A TEM sample preparation method including: placing a thin sample on a sample holder so that a first side surface of the thin sample which is closer to a desired observation target is opposed to a focused ion beam column; setting a processing region, which is to be subjected to etching processing by a focused ion beam so as to form a thin film portion including the observation target and having a thickness direction substantially parallel to a thickness direction of the thin sample, to a region of the first side surface that is adjacent to the thin film portion; and performing the etching processing to a portion of the thin sample extending from the first side surface thereof to a front surface thereof by irradiating the processing region with the focused ion beam from the focused ion beam column.