To reduce the amount of an embedding agent, shorten the focused ion beam(FIB) process time and surely hold powder particles, by setting a recessed part opened in the thicknesswise direction of a most end part of a plate-like substrate and holding a powder material in the recessed part by means of the embedding agent.

The recessed part 12 for holding (storing) a powder sample- embedding agent opened in the thicknesswise direction fw is formed at a most end part of a semicircular plate-like substrate 11 comprising plate parts 11a, 11b. A leading end of a projecting part 13 forming each edge of the recessed part 12 is a linear or curved angular part (sharp part) 13l. When a powder sample 2 is held by means of an embedding agent such as a liquid resin 3 or the like in the recessed part 12, the thickness of the embedding agent in the thicknesswise direction fw of the substrate is reduced because of a surface tension. Therefore, in making an observation part of the powder sample thin film, an abrasion thickness of the embedding agent can be made smaller and powder particles can be made thin film quickly and easily.