A fiber structure includes a first fiber layer including first reinforcement fiber bundles extending in a first yarn main axis direction, a second fiber layer including second reinforcement fiber bundles extending in a second yarn main axis direction that is orthogonal to the first yarn main axis direction, and auxiliary yarns that join the first fiber layer with the second fiber layer in a stacking direction of the first fiber layer and the second fiber layer. At least either one of the first reinforcement fiber bundles and the second reinforcement fiber bundles each include a core yarn and a covering yarn spirally wound around the core yarn. A covering angle, which is an orientation angle of the covering yarn, corresponds to a direction that differs from the first yarn main axis direction and the second yarn main axis direction and exhibits dynamic properties in a fiber-reinforced composite that uses the fiber structure as a reinforcement base.