To provide a joining method for skeleton members requiring no complicated work for the skeleton members, and requiring no joint member and the like for inter-skeleton-member joining.

Respective end parts of a sash 2, a transverse frame 3, and a longitudinal frame 4 are engaged with engaging grooves 11, 12, 13 formed in a casting mold 6 to set the sash 2, the transverse frame 3 and the longitudinal frame 4 in the mold 6. Molten metal W is poured inside the mold 6 upto a height level where respective tip parts of the sash 2, the transverse frame 3 and the longitudinal frame 4 are immersed completely into the molten metal W. After the molten metal W is poured in, the metal W is cooled for a prescribed time to be solidified. The mold is released after the metal W is solidified, and a cast joining member 5 is manufactured in a condition where the respective tip parts of the sash 2, the transverse frame 3 and the longitudinal frame 4 are coordinate cast, and a joining structure 1 is formed thereby.