A method for multiplex microorganism detection which is a method for detecting microorganisms including Listeria monocytogenes, pathogenic Escherichia coli 0157 and Salmonella spp. in foods, by amplifying a plurality of target genes in a single PCR reaction tube, comprising the following steps: a step for culturing microorganisms under such culture conditions as allowing the proliferation of each microorganism of pathogenic Escherichia coli 0157, Salmonella spp., and Listeria monocytogenes for 18 h or more in a medium with a concentration of phosphate-buffer solution of 50 mM or more or having a buffer ability, which is similar to the one of a medium having a concentration of phosphate-buffer solution of 50 mM or more; a step for extracting DNA of the target microorganisms to be detected, by treating with at least a lytic enzyme and /or a bacteriocin having a lytic activity, further treating with a surfactant and a protein-denaturing agent; and a step for carrying out Multiplex PCR after having mixed a combination of (i) a DNA selected from the group consisting of primer sets for pathogenic Escherichia coli O157: SEQ ID Nos: 1 and 2, SEQ ID Nos: 7 and 8, SEQ ID Nos: 11 and 12, and SEQ ID Nos: 13 and 14, (ii) a DNA selected from the group consisting of primer sets for Salmonella spp.: SEQ ID Nos: 3 and 4, SEQ ID Nos: 9 and 10, and SEQ ID Nos: 15 and 16, and (iii)a DNA selected from the group consisting of primer sets for Listeria monocytogenes: SEQ ID Nos: 5 and 6, SEQ ID Nos: 17 and 18, and SEQ ID Nos: 19 and 20, as primer sets. a step for culturing microorganisms under such culture conditions as allowing the proliferation of each microorganism of pathogenic Escherichia coli 0157, Salmonella spp., and Listeria monocytogenes for 18 h or more in a medium with a concentration of phosphate-buffer solution of 50 mM or more or having a buffer ability, which is similar to the one of a medium having a concentration of phosphate-buffer solution of 50 mM or more; a step for extracting DNA of the target microorganisms to be detected, by treating with at least a lytic enzyme and /or a bacteriocin having a lytic activity, further treating with a surfactant and a protein-denaturing agent; and a step for carrying out Multiplex PCR after having mixed a combination of (i) a DNA selected from the group consisting of primer sets for pathogenic Escherichia coli O157: SEQ ID Nos: 1 and 2, SEQ ID Nos: 7 and 8, SEQ ID Nos: 11 and 12, and SEQ ID Nos: 13 and 14, (ii) a DNA selected from the group consisting of primer sets for Salmonella spp.: SEQ ID Nos: 3 and 4, SEQ ID Nos: 9 and 10, and SEQ ID Nos: 15 and 16, and (iii)a DNA selected from the group consisting of primer sets for Listeria monocytogenes: SEQ ID Nos: 5 and 6, SEQ ID Nos: 17 and 18, and SEQ ID Nos: 19 and 20, (i) a DNA selected from the group consisting of primer sets for pathogenic Escherichia coli O157: SEQ ID Nos: 1 and 2, SEQ ID Nos: 7 and 8, SEQ ID Nos: 11 and 12, and SEQ ID Nos: 13 and 14, (ii) a DNA selected from the group consisting of primer sets for Salmonella spp.: SEQ ID Nos: 3 and 4, SEQ ID Nos: 9 and 10, and SEQ ID Nos: 15 and 16, and (iii)a DNA selected from the group consisting of primer sets for Listeria monocytogenes: SEQ ID Nos: 5 and 6, SEQ ID Nos: 17 and 18, and SEQ ID Nos: 19 and 20,