An oil supply device for an engine includes a first oil suction passage, a second oil suction passage, a first pump for sucking and discharging oil from the first oil suction passage, a second pump arranged in series with the first pump, the second pump for sucking and discharging oil from at least one of the first pump and the second oil suction passage, a check valve for blocking oil circulation, a first oil passage, a second oil passage, a third oil passage for establishing communication between the first oil passage and the second oil passage, and a supply volume control device for varying oil supply volume to a lubrication system portion, to a cooling system portion, or to the lubrication system portion and the cooling system portion in accordance with a change in at least one of an engine oil temperature, an engine rotation speed, and an engine load.