A gear transmission device includes a transmission mechanism, and a gear backlash adjusting mechanism engaged with the transmission mechanism. The transmission mechanism includes a first adjusting gear and a second adjusting gear meshing together. The adjusting mechanism includes a fixing plate and an adjusting member sleeved on the first adjusting gear. The fixing plate defines a limiting hole. The adjusting member comprises a flange received in the limiting hole. A maximum distance from an edge of the flange near the second adjusting gear to the rotation shaft of the first adjusting gear is greater than a minimum distance from an end of the flange away from the second adjusting gear to the rotation shaft of the first adjusting gear.