An apparatus for forming a hollow FRP article by internal pressure molding includes a vacuum chamber, a forming die positioned in the vacuum chamber, a vacuum-chamber opening/closing mechanism, a composite-body support device for supporting a composite body without making the composite body come into contact with the forming die in a state where the forming die is opened by the vacuum-chamber opening/closing mechanism, the composite body including an airtight internal-pressure holding tube and a prepreg fitted on said airtight internal-pressure holding tube, an evacuation system for evacuating the vacuum chamber, an internal-pressure supplying device for applying pressure to an inside of the internal-pressure holding tube, and a controller for actuating the vacuum-chamber opening/closing mechanism to clamp the forming die to thereby bring the forming die and the composite body into intimate contact with each other.