A lubricating device for a four-stroke engine is provided that circulates oil while lubricating each part in a valve operating chamber and a crank chamber by supplying the oil to the valve operating chamber and the crank chamber using pressure fluctuation in the crank chamber, the pressure fluctuation being caused by reciprocating motion of a piston. The valve operating chamber is formed by mounting a valve operating chamber cover, and a suction passageway that sucks the oil in the valve operating chamber is provided by forming a groove on an inner surface of the valve operating chamber cover and sealing the groove with a sealing member shaped to fit the groove.