Transmission

The transmission comprises drive gears (43-45) provided on a main shaft (41) to be non-rotatable relative to each other, and driven gears (46-48) respectively meshed with the drive gears are supported by a cylindrical gear supporting portion (42a) of a countershaft (42) to be rotatable relative to each other, and a slide shaft (72) capable of selectively engaging with one of the driven gears (46-48) is axially movably inserted in the gear supporting portion (42a) to be non-rotatable relative to the countershaft (42). A shaft driving member (75) configured to axially drive the slide shaft (72) is disposed to coaxially surround the slide shaft (72).