A linear transmission device includes a shaft, a moving member movably provided on the shaft, and a lubrication unit provided at the moving member. The lubrication unit has a lubricant container and a block. The lubricant container has a storage space which communicates with the interior of the moving member via a lubricant dispensing opening. The block is provided in the storage space of the lubricant container and can be displaced by an inertial force generated by movement of the moving member so that, during its displacement, the block squeezes the lubricant in the storage space, thereby driving the lubricant into the interior of the moving member through the lubricant dispensing opening for lubrication.