An apparatus to accurately detect a force acting on a tire, based on a stress acting on a connection mechanism that connects a wheel and a wheel support member. A tire-acting-force detection apparatus is applied to a vehicle including a wheel unit composed of a wheel and a tire held at an outer circumferential portion of the wheel; a wheel support member which supports the wheel by a wheel support portion perpendicular to a rotation axis such that the wheel can rotate about the rotation axis; and a connection mechanism which connects a circular plate portion of the wheel and a wheel support portion of the wheel support member at a plurality of positions separated from one another about the rotation axis. The tire-acting-force detection apparatus includes a plurality of detection elements detecting stresses acting on each bolt, and an electronic circuit apparatus calculating a tire acting force, which acts at the ground contact point of the tire, based on the detected stresses.