PURPOSE: To improve the low temperature starting property of a Diesel engine and the like by providing a means for detecting engine start and a means to open an air intake valve in the exhaust stroke when said start is detected through said detecting means.

CONSTITUTION: Since both signals of the engine rotation and engine temperature supplied from a rotation sensor 15 and a temperature sensor 16 to a controller 14 at a low temperature start of the engine are below the predetermined values, an electromagnetic 3-way valve 13 is placed in ON state and the discharge port of an oil pump 12 and the oil supply port of an oil tappet 10 are put and kept in communication with each other. Accordingly, when a starter motor is operated and the oil pump 12 is driven, oil is supplied to the oil tappet 10, which is then extended and fixed to the maximum extent, resulting in disappearance of a valve gap. From the above, since an air intake valve 5 is opened even in the last stage of an exhaust stroke, a part of air raised in its temperature flows backward into an air intake passage 6 and is sucked into a combustion chamber 4 again in the intake stroke.