Type Ia Supernovae (SNe Ia) are believed to be thermonuclear explosions of a white dwarf, and are one of the most mature cosmological standardized candles. However, the explosion mechanism has not yet been fully understood. Furthermore, origins of their observational diversities are yet to be clarified. In this talk, it is argued that an asymmetry in the explosion is likely a generic feature of SNe Ia, and that the diversity arising from various viewing angles can be an origin of at least a part of the observational diversities. Late-time optical nebular spectra show variations in the wavelengths of some lines, suggesting the asymmetric ignition process. Using the wavelength shift as a marker of the viewing direction, there is a correlation between this value and the so-called velocity gradient, indicating that the spectroscopic diversity in the velocity gradient is caused by the viewing angle effect. The maximum B-V color is also related to the viewing direction in this interpretation, indicating that at least a part of variations seen in the peak color is intrinsic, rather than coming from environment effects. These effects should be taken into account in the future precise measurement of cosmological parameters using SNe Ia.