Abstract: An automatic transmission having Ravigneaux Type planetary gear unit comprises a first and a second sun gear, a long pinion meshing the first sun gear, a short pinion meashing the long pinion and the second sun gear, a carrier supporting the long pinion and the short pinion and a ring gear meshing the long pinion;the input shaft connects the second sun gear through a first clutch, and connects the first sun gear through a second clutch;the output member is located in the center of the automatic transmission mechanism so that the output member encloses the input shaft;in case of three speed transmission mechanism, a first clutch is located axially and extreme outside the transmission mechanism;in case of four speed transmission mechanism a third clutch is located axially and outside the first clutch.