We analyzed the stomach contents of wild boars (Sus scrofa) inhabiting evergreen forests in western Japan and found that they were dependent on the masting of acorns of Castanopsis cuspidata. The increased availability of C. cuspidata acorns positively affected their consumption by wild boars. In the good mast years, wild boars consumed C. cuspidata acorns from November to June of the following year. No significant annual variation in body condition was detected, suggesting that alternative food resources (e.g., bamboo shoots) may have maintained the body condition of wild boars, even in poor mast years. A strong negative correlation was found between the consumption of C. cuspidata acorns and the amount of crop damage to vegetables. This study revealed the wild boar as a pulsed food resource feeder, which has not yet been identified in Japan, and emphasized the importance of considering C. cuspidata masting for designing effective strategies for mitigating crop damage.