We have investigated the deformation mechanism of ruby in a microscopic area using a femtosecond laser having a pulse width, wavelength, and repetition rate of 238 fs, 780 nm, and 1 kHz, respectively. Transmission electron microscope observation revealed that a specific oblique pattern originating from cracks having a width of approximately 10 nm formed at the focal point. The peak shift of ruby fluorescence indicated the existence of a residual stress of 0.11 GPa at the irradiated area. Considering the pattern and magnitude of the residual stress at the focal point, we suggest that the crack propagated along the {1102} rhombohedral planes and the {1100} planes by laser irradiation.