Beam frame assembly having joint device

A joint device includes a main fixing plate, an auxiliary fixing plate, and a fastener. The main fixing plate has a vertical wall disposed between a longitudinal beam and a transverse beam, a first extending wall extending towards a side of the longitudinal beam from the vertical wall and crossing over and abutting against an upper portion of the longitudinal beam, and a second extending wall extending towards a side of the transverse beam from the vertical wall and crossing over and abutting against a lower portion of the transverse beam. The auxiliary fixing plate is disposed in an open groove of the transverse beam in a way that the transverse beam is clamped between the auxiliary fixing plate and the vertical wall of the main fixing plate. The fastener secures the longitudinal beam, the transverse beam, the main fixing plate and the auxiliary fixing plate together.