To automate assembly of an inner partition to be used at the time of filling and packaging products such as bottles and cans into a corrugated fiberboard case or the like by inserting a vertical partition into a specified number of groove guides to make it stand and transferring them, and by lowering a lateral partition to be completely coupled with the vertical partition during the transfer process.

A specified number of groove guides 2a, 2b, 2c are provided toward an advancing direction with specified intervals, vertical partitions 1a, 1b, 1c with a cut upward are respectively inserted to stand, and they are transferred to a lateral partition supply part by a transfer lever 4. Then lateral partitions 5a, 5b, 5d, 5e with a cut downward are inserted into the vertical partitions 1a, 1b, 1c to the upper end of the groove guides 2a, 2b, 2c, and they are supplied onto a bottom plate 17 provided at a terminal point of the groove guides 2a, 2b, 2c in an incomplete engaged state. Then the lateral partitions 5a, 5b, 5d, 5e are lowered together by a lowering plate 6 from above to complete inner partitions completely coupled.