We built a device that uses millimeter waves to monitor the water/ice state of samples. It consists of a 35-GHz Gunn oscillator producing an output power of about 10 mW, two horn antennas, and a power meter. We confirmed that the difference in the absorption of water and ice was significant, and we could discriminate and monitor the frozen states of water and cell medium containing dimethyl sulfoxide (DMSO). We also measured the absorption of frozen cell media containing different DMSO concentrations. These experiments demonstrate the possibility of applying millimeter waves to optimize and monitor crystal structure for various combinations of cell medium and DMSO.