To provide a detector and a method for detecting force acting on a tire capable of finding torque and grounding reaction (vertical force) by only computation from a sensor output, while securing axial-directional strength.

Axle side connection parts 2 and wheel side connection parts 3 are arranged alternately in positions divided uniformly into four along a circumferential direction concentric with the rotation center, in a rotor 4, an area constituted of an elastically deformable member is provided between each of the axle side connection part 2 and each of the wheel side connection part 3, ceramic load sensors 5 are provided in intermediate positions in the four areas A, B, and the force acting on the tire is detected based only on detection values from a load sensor group comprising the four load sensors 5.