For studying thermal properties of superconducting niobium, it is necessary to provide temperatures within a range of 1.4 to 10 K and adequate aids for their measuring. An error of temperature measurements must not exceed 1 mK. Types of thermometers used at low temperatures are examined. Zirconium oxynitride is chosen as the basic thermometer material. An algorithm for measuring is proposed which makes it possible to reduce errors of temperature measuring and improve its accuracy.