A vehicle side body structure including: a side sill having a substantially closed cross-sectional structure extending in a vehicle longitudinal direction; and a center pillar having a substantially closed cross-sectional structure extending in a substantially upward direction from said side sill, wherein an opening (2f, 2r) is formed at a position above the side sill and on each of front and rear sides of the center pillar, wherein the center pillar includes a pillar inner and a pillar outer, wherein the pillar inner has a pillar inner upper and a pillar inner lower, wherein the pillar inner lower is provided on a lower side of the pillar inner upper, wherein in a longitudinal direction of the side sill, in a center pillar arrangement region where the center pillar is located, the pillar inner upper and the pillar inner lower overlap each other inside a closed cross section of the side sill in a vehicle side view, wherein a section (22F, 22R) configured to at least partially partition the inside of the closed cross section in the longitudinal direction is provided inside the closed cross section, and wherein the section (22F, 22R) is joined to an overlapping portion between the pillar inner upper and the pillar inner lower and to an inner surface, which faces the inside of the closed cross section, in the side sill wherein a plurality of sections (22F, 22R) is separately provided on front and rear sides of the overlapping portion, characterized in that each of the plurality of sections (22F, 22R) provided on the front and rear sides is arranged on an outer side of the overlapping portion in the vehicle width direction, and wherein each of the plurality of sections (22F, 22R) is only joined to one of the pillar inner upper and the pillar inner lower, located on the outer side in the vehicle width direction in the overlapping portion. a side sill having a substantially closed cross-sectional structure extending in a vehicle longitudinal direction; and a center pillar having a substantially closed cross-sectional structure extending in a substantially upward direction from said side sill, wherein an opening (2f, 2r) is formed at a position above the side sill and on each of front and rear sides of the center pillar, wherein the center pillar includes a pillar inner and a pillar outer, wherein the pillar inner has a pillar inner upper and a pillar inner lower, wherein the pillar inner lower is provided on a lower side of the pillar inner upper, wherein in a longitudinal direction of the side sill, in a center pillar arrangement region where the center pillar is located, the pillar inner upper and the pillar inner lower overlap each other inside a closed cross section of the side sill in a vehicle side view, wherein a section (22F, 22R) configured to at least partially partition the inside of the closed cross section in the longitudinal direction is provided inside the closed cross section, and wherein the section (22F, 22R) is joined to an overlapping portion between the pillar inner upper and the pillar inner lower and to an inner surface, which faces the inside of the closed cross section, in the side sill wherein a plurality of sections (22F, 22R) is separately provided on front and rear sides of the overlapping portion, characterized in that each of the plurality of sections (22F, 22R) provided on the front and rear sides is arranged on an outer side of the overlapping portion in the vehicle width direction, and wherein each of the plurality of sections (22F, 22R) is only joined to one of the pillar inner upper and the pillar inner lower, located on the outer side in the vehicle width direction in the overlapping portion.