A non-invasive, unstaining tissue measurement method is expected to be an important tool for regenerative medical. As THz wave do not affect biological tissue because of their low energy, THz measurement method is expected to become a new modality of biomedical analysis as a noninvasive diagnosis. Due to the fact that biological tissues possess high level of hydration, it results in strong absorption at terahertz frequencies. A ridge waveguide LiNbO<sub>3</sub> based nonlinear terahertz generator was used to achieve high output power for THz time domain spectroscopy (THz-TDS). A ridge waveguide was designed for high efficiency emission from the LiNbO<sub>3</sub> crystal by the electro-optic Cherenkov effect. This THz-TDS system has realized six orders of dynamic range, and the bandwidth of the spectrum reaches 7 THz in the upper limit. We measured a reflected terahertz pulse shape at the interface between a plastic culture dish and biological tissues. By studying the gradient of phase spectroscopy of reflected THz pulse, we have been able to differentiate between human fibroblast tissue and cancer tissue. We demonstrate the application of terahertz time domain spectroscopy pulse in reflection geometry for the non-distractive measurement of biological tissues cultured on a plastic culture dish. These results demonstrate the potential of terahertz phase information for the study of biological tissues.