The present study examined the locus responsible for the effect of emotional state on sentence processing in healthy native speakers of Japanese, using event-related brain potentials. The participants were induced into a happy, neutral, or sad mood and then subjected to electroencephalogram recording during which emotionally neutral sentences, including grammatical sentences (e.g. window-NOM close "vi," "The window closes."), morphosyntactically-violated sentences (e.g. window-ACC close "vi," Lit. "Close the window."), and semantically-reversed sentences (e.g. window-NOM close "vt," "The window closes 'pro.'") were presented. The results of the ERP experiment demonstrated that while the P600 effect elicited by morphosyntactic violation was not modulated by mood, the P600 effect elicited by semantic reversal anomaly was observed only in participants previously induced into a happy mood. The LAN and N400 were not sensitive to the participants' transient emotional state. These results suggest intact memory access and impaired integration of syntactic and semantic information in individuals in a sad mood.