Flexural rigidity and deflection characteristics of rice stalks were examined in order to make clear the mechanical interaction between a rice stalk and a combine reel in harvesting. Deflection of a rice stalk caused by reel operation is so large that conventional equation of small deflection for elastic beam cannot be adapted to a presumption of a deflection characteristics. Therefore, equation of large deflection for elastic beam were introduced to solve this problem. Availability of this equation was examined by comparison with the measuring results of piano wire, and relationship between deflection and load acting on a rice stalk was presumed by this equation. As a result, measuring results corresponded to predicted ones considerably. Furthermore, the flexural rigidity of rice stalk varied on the direction of height, was discussed.