A high-pressure trunnion ball valve which is particularly suitable for a high-pressure fluid, the high-pressure trunnion ball valve is composed of a ball (10) rotatably provided in a body (3) having a lid member (2), a seat retainer (11) seal-connected to the ball, a spring member (12) applying an elastic force to the seat retainer to a seal side, and a seal member (13) attached to an outer circumferential face of the seat retainer. An upper stem (50) and a lower stem (51) having the same diameter are provided on an upper side and a lower side of the ball in an extending manner, respectively, to constitute a ball member (52), shaft-attaching seal mechanisms (20) having the same structure are attached to the upper and lower stems at symmetrical positions regarding the ball to achieve a balance structure, thereby avoiding thrust loads.