TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In the method: where a transcription regulator of methionine synthetic pathway is weakened or inactivated; a biosynthetic pathway of threonine is suppressed; and a gene expression of thrA is enhanced. The expression of endogenous homoserine O-succinyltransferase encoded by metA gene, endogenous cystathionine gamma synthase encoded by metB gene, endogenous transcription regulator of methionine synthetic pathway encoded by metJ, endogenous O-acetylhomoserine sulfhydrylase encoded by metY gene, endogenous O-succinylhomoserine sulfhydrylase encoded by metZ gene, and/or endogenous homoserine kinase encoded by thrB gene, is suppressed. Preferred Components: The homoserine O-acetyltransferase is encoded by a gene comprising Corynebacterium glutamicum, Leptospira meyeri, Deinococcus radiodurans, Pseudomonas aeruginosa or Mycobacterium smegmatis. The homoserine O-acetyltransferase has the amino acid sequence of Unipro database No. Q9RVZ8 (SEQ ID NO: 32) (Sequences not defined), GenBank Accession No. NP 249081 (SEQ ID NO: 33) (Sequences not defined) or YP 886028 (SEQ ID NO: 34) (Sequences not defined). The aspartokinase or homoserine dehydrogenase peptide has: a mutation at amino acid position 345; and SEQ ID NO.27 (containing a fully defined sequence of 820 amino acids, as given in the specification). The microorganism is an Escherichia species, preferably Escherichia coli. The microorganism: is derived from L-threonine, L-isoleucine or L-lysine producing strain; and has at least one of endogenous cystathionine gamma synthase, endogenous O-succinylhomoserine sulfhydrylase, or endogenous O-acetylhomoserine sulfhydrylase of which the activity is reduced, inhibited or inactivated, or the microorganism does not have an endogenous gene encoding cystathionine gamma synthase, an endogenous gene encoding O-succinylhomoserine sulfhydrylase, or an endogenous gene encoding O-acetylhomoserine sulfhydrylase. The activity of homoserine kinase is reduced, inhibited, or inactivated, or the microorganism does not have an endogenous gene encoding homoserine kinase. The microorganism is derived from the threonine producing strain: Escherichia coli MF001 free from methionine-dependency (Accession No: KCCM 10568); or Escherichia coli FTR2533 (Accession No: KCCM 10541). The microorganism is: Escherichia coli CJM-X(pthrA(M)-CL), prepared by transforming CJM-X strain (KCCM 1092IP) with a thrA expression vector; or Escherichia coli CJM2-X(pthrA(M)-CL), prepared by transforming CJM2-X strain (KCCM 10925P) with a thrA expression vector. EXAMPLE - No suitable example given.