A hydraulic supply device of an automatic transmission, which supplies operating oil to the automatic transmission that is able to shift power from an engine and transmit the power to drive wheels of a vehicle by selectively engaging a plurality of frictional engagement devices using hydraulic pressure is disclosed. The hydraulic supply device includes: an accumulator that accumulates operating oil; a leaking flow compensation hydraulic pump that supplies the operating oil for compensating for a flow rate of the operating oil leaking in the automatic transmission to the automatic transmission by being driven by a power source different from the engine when the engine is automatically stopped; and a hydraulic supply control mechanism configured to supply the operating oil accumulated in the accumulator to a starting frictional engagement device that is one of the plurality of frictional engagement devices to be engaged at the time of starting the vehicle when the engine is restarted after the engine is automatically stopped.