Cylinder rest internal combustion engine

To provide a cylinder rest internal combustion engine which does not need a high response performance in operating a throttle valve (TH) and which can eliminate output variations in the case of variations in the number of cylinders. In a cylinder rest internal combustion engine with some of a plurality of cylinders being restable, all the cylinders are divided into a plurality of cylinder groups, each of the cylinders is provided with an independent throttle valve (TH), an ECU (70) as a cylinder number control unit for increasing the number of operative cylinder groups according to at least the grip opening is provided, and motors (21A, 21B) for bringing into a fully closed state the throttle valves in the cylinder in the rest state on the basis of each cylinder group, a throttle valve opening sensor (22) and the like are provided.