To provide a lubricating device of a transmission, for improving the lubrication performance of a bearing that supports a counter shaft of a transmission while simplifying the structure of the lubricating device.

In the lubricating device of a transmission, a groove portion, which extends upward from the bearing, is formed on a sidewall of a transmission casing to which the bearing is mounted, and a concave portion to reserve a lubricating oil and a discharge passage to make the lubricating oil outflow from the concave portion are formed on a detent plate. The device is configured in such a manner that when a manual shaft is at a stop position, the discharge passage is closed by the sidewall of the transmission casing to reserve a lubricating oil dropping from above in the concave portion, and that when the manual shaft is moved from the stop position to an advancing position or a reverse position, the discharge passage is opened above the groove portion to make the lubricating oil reserved in the concave portion flow to the groove portion.