The invention relates to a tension adjusting device used for transmission equipment. The tension adjusting device comprises a swing arm and a tensioning component, wherein the swing arm is rotatably fixed through a fixing component, the tensioning component is rotatably fixed on the swing arm, the swing arm is provided with a swing arm shaft, a hole is formed in the swing arm shaft, the fixing component is assembled in the hole, a bearing component is arranged between the fixing component and the hole, a first sealing cover is arranged at the end part position of the fixing component, a static electricity releasing component is arranged between the first sealing cover and the swing arm shaft, and a static electricity releasing route is formed by the fact that the static electricity releasing component is in contact with the first sealing cover and the swing arm shaft. The static electricity generated in the operating process of the tension adjusting device can be eliminated due to the structure of the tension adjusting device.