To provide a backboard for a back carry bag which has good air permeability, matches the shape of the back, and widely disperse a load of the bag.

The backboard includes a base board 1, a seat part 2 set on the upper face of the base board 1, a plurality of projecting parts 3a provided on the upper face of the seat part 2, recessed parts 3b formed between projecting parts 3a, and a groove shaped main air passage 4 formed in the vertical direction at the center of the base board 1 and dividing the seat part 2 into right and left. The groove-shaped main air passage 4 is opened at upper and lower sides and the projecting parts 3a are vertically disposed in rows on right and left sides of the main air passage 4. Because the recessed parts 3b form air passages in the lateral direction and communicates with the groove shaped main air passage 4 vertically formed in the center, the ventilation in the vertical and lateral directions of the backboard are secured to reduce stuffiness. Because the projecting parts 3a are set on both right and left sides of the main air passage 4 set on the center of the baseboard 1, a load of the back carry bag is dispersed on right and left sides and shouldering feeling is improved.