The objective of this study is to evaluate the value of flexibility for cropping system with greenhouse facilities that farmers can take contingent on market condition. A concept of switch option, a kind of Real Options(RO) approach, is adopted to evaluate the option value of flexible cropping system. For the simplicity, region is limited to Chungbuk province and crops for cropping systems are limited to watermelon and melon. Prices of both crops are assumed as stochastic variables and proved to follow mean-reverting process. Results show that farmers choose crops based on relative prices for the first crop. On the other hand, watermelon is hardly chosen for the second crop because the price of watermelon far below than that of melon. The value of flexibility, defined as the difference of the value of flexible cropping system and the value of inflexible cropping system, is 1,583 thousand won during three business years. Sensitivity analysis show that the flexibility value increases with melon production and volatility of melon and decreases with production cost of melon. The results imply that the value of flexibility for cropping system should be reflected in the investment analysis of fruit vegetable farming with greenhouse facilities.