facing drive shaft 13 is increased in diameter and the outer periphery thereof is provided with ratchet teeth 34 the free end of drive shaft 13 on the other hand is provided with an integral drive plate 35 extending radially outwardly at right angles to drive shaft 13 and retained thereon by a nut 36 a pawl 37 is pivoted by a pin 38 to a peripheral edge portion of drive plate 35 when pawl 37 meshes with one of the teeth 34 and the spring force stored in spiral spring 31 is released starter shaft 30 is rotated this torque is transmitted through ratchet teeth 34 and pawl 37 to drive plate 35 so as to cause rotation of drive shaft 13 integral with drive plate 35 for starting the internal combustion engine 10 after the engine has been started drive shaft 13 is thereby rotated at a high speed so that pawl 37 is caused to move pivotally about pin 38 by centrifugal forces and is thus released from meshing engagement with ratchet teeth 34 to ensure the driving of drive shaft 13 while in the present embodiment the starting system for the internal combustion engine is of the type using a foot pedal starter shaft 30 and spiral spring 31 for manually storing and releasing the spring force the automatic transmission according to the invention which is described hereinbelow is also applicable to kick starters or starters using starter motors as generally employed for motorcycles a first clutch 40 of the centrifugal type serves as a starter clutch and the inner members 41 thereof are pivoted by respective pins 43 to peripheral.