A vehicle transmission includes a shift lever including a receiving unit formed therein, a bullet in which at least a portion thereof is inserted and disposed within the receiving unit of the shift lever, and a detent groove unit which allows the bullet to advance or retreat depending on a profile of a contact surface in contact with the bullet as the shift lever rotates. The bullet includes a guide aperture formed longitudinally along an advancement-retreat direction of the bullet, and a fixing pin having at least one end thereof fixed to the receiving unit is inserted into the guide aperture.