When pulling and growing a single crystal from a raw material melt by the Czochralski method, a boundary between the single crystal and the raw material melt is imaged by an optical sensor, and also the weight of the single crystal is measured by a weight sensor, a diameter value of the single crystal is calculated on the basis of first measured values of the diameter of the single crystal derived from image data captured by the optical sensor and second measured values of the diameter of the single crystal derived from weight data captured by the weight sensor, and a pulling rate of the single crystal and the temperature of the raw material melt are adjusted on the basis of the calculated diameter value to thereby control the diameter of the single crystal, and thus it is possible to accurately measure the diameter of a growing single crystal.