PURPOSE: To obtain a fine structural body of a triangular shape by superposing the band-shaped regions irradiated between irradiations of a first time and a second time at the boundary between a resist layer and a substrate and using a mask having perpendicular walls.

CONSTITUTION: The resist layer 4 on the conductive substrate 5 is turned by an angle (+α) from the surface parallel with a mask plane around a turning axis 6. The beam failing to be absorbed by the mask advances into the band-shaped regions 7 within the resist layer 4. The resist layer 4 is turned by an angle (-α) with respect to the mask plane around the turning axis 6 and the band-shaped regions 8 of the resist layer 4 are irradiated again at the irradiation of the second time. The band-shaped regions 7 and 8 overlap on the surfaced of the resist layer at the boundary between the resist layer 4 and the substrate 5. Then, not only the irradiated regions are removed but the non-irradiated regions 9 having the band-shaped structure of the triangular section are dropped and peeled at the time of development. As a result, the fine structural body of the triangular section is obtd. by using the mask having the perpendicular walls.