This invention relates to the Agrobacterium bacterium to be used in plant transformation method comprising three types of plasmids. The Agrobacterium bacterium of this invention comprises plasmids of (1) to (3) shown below:(1) a plasmid comprising the following components:(i) the virB gene, the virC gene, the virD1 gene, the virD2 gene, the virD3 gene, the virG gene and the virJ gene of pTiBo542, and(ii) an origin of replication(2) a disarmed Ti plasmid or a disarmed Ri plasmid of Agrobacterium bacterium and(3) a plasmid having a T-DNA region consisting of a desired DNAwherein each of the plasmids of (1) to (3) has a replication mechanism that enables a mutual coexistence with each other.
