To provide a transmission capable of setting many change gear stages without increasing components such as a gear.

This transmission 1 for changing a speed of the driving force from a power source in stages with a plurality of predetermined change gear ratios different from each other, comprises a first shaft 21 to which the driving force is input, second and third shafts 22, 23 mounted in parallel with the first shaft 21, a fourth shaft 24 connected with the second and third shafts 22, 23 and outputting the driving force, a first integrated gear GI1 having a pair of first and third gears a, c and a pair of second and fourth gears b, d respectively mounted between both shafts 22, 23, and mounted on the first shaft 21, a first clutch S1 for selectively connecting/disconnecting the first integrated gear GI1 to the first shaft 21 to change a speed of the driving force input to the first integrated gear GI1, and second and third clutches S2, S3 for selectively connecting/disconnecting any one of pairs of first to fourth gears a to d to the second and third shafts 22, 23.