A column/beam joint structure, made of steel members, in which a reinforcing member formed into a flat plate or into a strip shape so as to surround the outer periphery of the flange is interposed between a flange having a vertical plane constituting the column and a base plate constituting a connector fixedly fitted to an end of a beam. The flange, the reinforcing member and the connector are integrally joined together via a connecting fastener member.
