The present invention provides a novel heterocyclic compound. A heterocyclic compound represented by general formula (1) wherein, R1 and R2, each independently represent hydrogen; a phenyl lower alkyl group that may have a substituent(s) selected from the group consisting of a lower alkyl group and the like on a benzene ring and/or a lower alkyl group; or a cyclo C3-C8 alkyl lower alkyl group; or the like; R3 represents a lower alkynyl group or the like; R4 represents a phenyl group that may have a substituent(s) selected from the group consisting of a 1,3,4-oxadiazolyl group that may have e.g., halogen or a heterocyclic group selected from pyridyl group and the like; the heterocyclic group may have at least one substituent(s) selected from a lower alkoxy group and the like or a salt thereof.