A trunnion-type ball valve, a valve seal structure, and a valve packing in which, a seal surface pressure of a tip outer peripheral region is improved. A ball (3) provided inside a body (2) is rotatably provided via upper and lower stems (4 and 5) and is sealed with a ball seat (6). The trunnion-type ball valve has a packing attached between an outer periphery step part provided at a rear part of the ball seat and the body and a pressing mechanism by which the packing is pressed to a ball direction, and is provided with a contact surface to be contacted with a step part surface of the outer periphery step part on a tip outer diameter side of the packing and a space provided between the packing and the step part surface of the outer periphery step part on a tip inner diameter side of the packing.