To obtain a sample which is changed little in structure by processing even when containing heavy elements partly and has a uniform process face by projecting a focused ion beam parallel to the surface of an object to be processed from a side face of the object to be processed, and forming the sample of a thin film for use in an electron microscope.

A semiconductor sample 15 has projecting parts 16 formed like stairs by a dicing saw 5. The sample is cut by the dicing saw 5 from a point separated by a predetermined distance from an observation part of the projecting part 16 in a direction orthogonal to a sample surface. An unnecessary semiconductor sample 15a is cut off and a focused ion beam(FIB) process face 19 is formed. The FIB process face 19 is marked by a laser or the like to recognize a transmission electron microscope(TEM) thin film sample part 17. The sample is loaded on a stage of an FIB apparatus so that an FIB 10 is irradiated at right angles to the FIB process face 19. While the marking on the FIB process face 19 is confirmed, a process area 18 is cut to leave the TEM thin film sample part 17 formed thin in a uniform thickness as an observation face.