To enhance lubrication performance of a bearing that supports the counter shaft of a transmission and to reduce stirring resistance of a lubricating oil to improve fuel consumption.

There is provided the lubricating device of a transmission in which an input shaft, a counter shaft and a drive shaft are disposed in parallel with one another in a transmission casing, the bearing of the counter shaft attached to the sidewall of the transmission casing is lubricated by scraping lubricating oil, and a detent plate is attached to a manual shaft above the counter shaft. In the lubricating device of a transmission, a groove is formed on the sidewall, the groove extending upward from the bearing and supplying the lubricant oil to the bearing, and a vertical wall part such that when the detent plate is at an advanced position, the top end of the vertical wall part opposes the sidewall in the front of the groove and that when the detent plate is at a reverse position, the top end opposes the sidewall behind the groove, is formed on the detent plate.