Pillar structure

A pillar structure comprising:

• a pillar inner panel extending in an up-down direction of a vehicle at a side part of the vehicle;
• and
• an outer reinforcement including a flange portion located at a more vehicle-outward position than the pillar inner panel in a vehicle-width direction, an outer portion located at a more vehicle-outward position than the flange portion, and a coupling portion coupling the flange portion to the outer portion, the flange portion being welded to the pillar inner panel, the outer portion having a thicknesses that varies in the up-down direction of the vehicle, the outer reinforcement forming a closed cross section with the pillar inner panel, wherein
• between a thick-plate region where a thickness of the outer portion is more than a predetermined thickness and the flange portion, the outer reinforcement has a plate-thickness gradual change region where a thickness of the outer reinforcement gradually changes in a front-rear direction of the vehicle such that a thickness of the flange portion becomes equal to or less than a thickness of the thick-plate region.