To observe the formation of ice lenses, unidirectional freezing experiments were carried out using a water-saturated porous medium made from micro glass particles. Knowledge of the ice configuration in the vicinity of a growing ice lens is important for clarifying the mechanism of the formation of ice lenses. The ice configuration in the vicinity of the warmest ice lens in the freezing porous medium was investigated by combining Raman spectroscopy with the unidirectional freezing experiments. No ice was found in any pore, warmer than the ice lens and the ice lens grows without penetrating the warmer pores.