A synchronizer-mechanism-equipped transmission capable of moving tips of sleeve teeth and ring teeth away from butting each other by moving a synchronizer sleeve with biasing means even if the tips of the sleeve teeth and ring teeth are in contact when actuator driving stops. When sleeve teeth of a synchronizer sleeve that moves during gear shifting are located at a first synchronization position where the sleeve teeth begin to come into contact with ring teeth, a pressing member of a detent mechanism is in contact with a pre-gear-shifting detent recessed portion of a star cam.