Handheld type four-cycle engine

With regard to a handheld type four-cycle engine including, in a side wall of a cylinder block, an intake valve, an exhaust valve and a valve operation mechanism operable in association with a crankshaft so as to open and close the above-mentioned valves and, an oil tank is formed in one side wall of the cylinder block, and the oil tank houses the valve operation mechanism and oil mist generation means for generating an oil mist from stored oil. It is thus possible to reliably lubricate the valve operation mechanism regardless of the operational position of the engine while allowing the size and weight of the engine main body to be reduced.