The thiourea compound according to claim 1, wherein R3 represents a group having the formula --(CH2)l --R4 in which l is an integer of 0 and R4 is a phenyl, naphthyl or pyridyl group optionally having 1-3 substituents selected from the group consisting of lower alkyl, lower alkoxy, phenoxy, lower alkylthio, hydroxy, halogen, nitro, cyano and trifluoromethyl.