Abstract: A power transmission device is provided with a gear mechanism, a case, an oil pump and an oil tank. The gear mechanism is arranged to operate in coordination with a drive source. The case houses the gear mechanism and stores oil for lubricating the gear mechanism. The oil pump is arranged to operate in coordination with the drive source so as to pump the oil stored in the case to lubricate the gear mechanism. The oil tank is arranged to collect a portion of the oil pumped from the oil pump. The oil tank includes a first discharge outlet arranged to discharge the oil collected in the oil tank to the case and a second discharge outlet arranged to discharge collected oil to the case when an amount of the oil collected in the oil tank is equal to or larger than a prescribed amount.