A power transmission device for a work vehicle includes a transmission case, a gear transmission housed in the transmission case and configured to transmit power to a travel device, and a transmission gear provided in the gear transmission in a state of sitting in lubricating oil stored in an internal space of the transmission case, the transmission case being provided with a wall part supporting a support shaft of the transmission gear in a state of being adjacent to the transmission gear, and the wall part being provided with a cover part protruding toward the outer periphery of the transmission gear from the wall part and covering the transmission gear.