An apparatus for optical second-harmonic generation (SHG) spectroscopy at the liquid/liquid interface has been constructed. The fundamental laser beam of 780–920 nm was irradiated to the interface under the total internal reflection condition, and the interfacial second-harmonic spectrum was obtained during 390–460 nm. An automatically wavelength-tuned Ti:Sapphire laser was employed in this study, and it was simultaneously controlled with other peripheral instruments, such as monochromator. The acquisition time per spectrum with 2 nm interval was less than 30 min. The measurement of SHG spectrum of water-soluble porphyrin adsorbed at the heptane/water interface was demonstrated. The solvatochromic shift of the SHG maximum of the adsorbed porphyrin was ascribed to the less polar environment around the porphyrin molecule at the interface in comparison with the aqueous phase.