A mutant microorganism having the ability to produce putrescine, wherein at least one gene selected from the group consisting of a speE gene encoding spermidine synthase, a speG gene encoding spermidine N-acetyltransferase, an argi gene encoding ornithine carbamoyltransferase chain 1-monomer and a puuP gene encoding putrescine importer, which are involved in the putrescine degradation or utilization pathway, is inactivated or deleted; and wherein at least one gene selected from the group consisting of a puuA gene encoding y-glutamylputrescine synthase, a ygjG gene encoding putrescine transaminase and an argF gene encoding ornithine carbamoyltransferase F is further inactivated or deleted; and wherein a promoter of at least one gene selected from the group consisting of an argECBH gene encoding an operon for arginine biosynthesis, an argD gene encoding acetyl ornithine aminotransferase, and a speF-potE gene encoding inducible ornithine decarboxylase and putrescine/ornithine antiporter is replaced with a promoter selected from the group consisting of a trc promoter, a tac promoter, a T7 promoter, a lac promoter and a trp promoter; and wherein the microorganisms are of Escherichia sp.