To provide a transmission capable of shifting in multi-stage for realizing smooth shifting, simplifying the structure, reducing the size and especially reducing in thickness by shortening the axial length.

Center gears A and B having rotation centers A', B' are arranged in different positions in the axial direction. Intermediate gear mechanism parts I-1 to I-5 for transmitting normal rotating force between the center gears A, B are provided with paired engagement gears a1 to a5 and b1 to b5 connected through clutches CL1 to CL5 to the center gears A, B to mesh with each other and rotate on the same axis. A reverse gear mechanism R for transmitting reverse rotating force included in the intermediate gear mechanism part I-3 is provided with a reverse engagement gear ar meshing with the engagement gear a3 meshing with the center gear A and a reverse engagement gear br connected through a clutch CLr to the gear ar to make a pair with the gear ar and rotate on the same axis and meshing with the center gear B. The clutches CL1 to CL5 are controlled to transmit the rotating force of forward 5-speed and backward 1-speed from the center gear A to the center gear B.